Single-Domain SR-TE その1(Explicit Path)
SR-TE & Explicit Path が理解できたので自分のメモ用にアウトプットします。
- 1. SR-TE & explicit path
- 2. Topology
- 3. Config
- 4．実装
- 4.3 Head-End(h_N1)
- 5. 検証
- 6. SR-TE はいつダウンするのか
- 7. 参考
1. SR-TE & explicit path
トラフィックの経路を明示的に定義するSR-TE
2. Topology
3. Config
h_N1（Head-End）
hostname h_N1
group CCIE-ISIS
router isis '.*'
is-type level-2-only
address-family ipv4 unicast
metric-style wide
segment-routing mpls
!
interface 'Gi.*'
point-to-point
address-family ipv4 unicast
!
!
interface 'Loopback .*'
address-family ipv4 unicast
!
!
!
end-group
!
interface Loopback0
ipv4 address 1.1.1.1 255.255.255.255
!
interface MgmtEth0/RP0/CPU0/0
shutdown
!
interface GigabitEthernet0/0/0/0
ipv4 address 10.1.2.1 255.255.255.0
!
interface GigabitEthernet0/0/0/2
ipv4 address 10.1.3.1 255.255.255.0
!
!
router isis 1
apply-group CCIE-ISIS
net 49.0001.0000.0000.0001.00
interface Loopback0
address-family ipv4 unicast
prefix-sid index 1
!
!
interface GigabitEthernet0/0/0/0
address-family ipv4 unicast
fast-reroute per-prefix
fast-reroute per-prefix ti-lfa
!
!
interface GigabitEthernet0/0/0/2
address-family ipv4 unicast
fast-reroute per-prefix
fast-reroute per-prefix ti-lfa
!
!
!
mpls oam
!
segment-routing
traffic-eng
segment-list EXPLICIT_LIST
index 10 mpls label 16003
index 20 mpls label 16002
index 30 mpls label 24365
index 40 mpls label 16005
index 50 mpls label 16006
!
segment-list PREF_75_EXPLICIT_LIST
index 10 mpls label 16003
index 20 mpls label 16005
index 30 mpls label 16006
!
policy EXPLICIT_PATH_POLICY
binding-sid mpls 24365
color 6 end-point ipv4 6.6.6.6
autoroute
include ipv4 6.6.6.6/32
!
candidate-paths
preference 75
explicit segment-list PREF_75_EXPLICIT_LIST
!
!
preference 100
explicit segment-list EXPLICIT_LIST
!
!
!
!
!
!
end
h_N2
hostname h_N2 group CCIE-ISIS router isis '.*' is-type level-2-only address-family ipv4 unicast metric-style wide segment-routing mpls ! interface 'Gi.*' point-to-point address-family ipv4 unicast ! ! interface 'Loopback .*' address-family ipv4 unicast ! ! ! end-group ! interface Loopback0 ipv4 address 2.2.2.2 255.255.255.255 ! interface MgmtEth0/RP0/CPU0/0 shutdown ! interface GigabitEthernet0/0/0/0 ipv4 address 10.1.2.2 255.255.255.0 ! interface GigabitEthernet0/0/0/1 ipv4 address 10.2.3.2 255.255.255.0 ! interface GigabitEthernet0/0/0/2 ipv4 address 10.2.4.2 255.255.255.0 ! ! router isis 1 apply-group CCIE-ISIS net 49.0001.0000.0000.0002.00 interface Loopback0 address-family ipv4 unicast prefix-sid index 2 ! ! interface GigabitEthernet0/0/0/0 ! interface GigabitEthernet0/0/0/1 ! interface GigabitEthernet0/0/0/2 address-family ipv4 unicast metric 1000 adjacency-sid index 365 protected adjacency-sid index 366 ! ! ! mpls oam ! segment-routing local-block 24000 25000 ! end
h_N3
hostname h_N3 group CCIE-ISIS router isis '.*' is-type level-2-only address-family ipv4 unicast metric-style wide segment-routing mpls ! interface 'Gi.*' point-to-point address-family ipv4 unicast ! ! interface 'Loopback .*' address-family ipv4 unicast ! ! ! end-group ! interface Loopback0 ipv4 address 3.3.3.3 255.255.255.255 ! interface MgmtEth0/RP0/CPU0/0 shutdown ! interface GigabitEthernet0/0/0/0 ipv4 address 10.1.3.3 255.255.255.0 ! interface GigabitEthernet0/0/0/1 ipv4 address 10.2.3.3 255.255.255.0 ! interface GigabitEthernet0/0/0/2 ipv4 address 10.3.5.3 255.255.255.0 ! interface GigabitEthernet0/0/0/3 ipv4 address 10.3.4.3 255.255.255.0 ! router isis 1 apply-group CCIE-ISIS net 49.0001.0000.0000.0003.00 interface Loopback0 address-family ipv4 unicast prefix-sid index 3 ! ! interface GigabitEthernet0/0/0/0 ! interface GigabitEthernet0/0/0/1 ! interface GigabitEthernet0/0/0/2 address-family ipv4 unicast metric 1000 ! ! interface GigabitEthernet0/0/0/3 ! ! mpls oam ! end
h_N4
hostname h_N4 group CCIE-ISIS router isis '.*' is-type level-2-only address-family ipv4 unicast metric-style wide segment-routing mpls ! interface 'Gi.*' point-to-point address-family ipv4 unicast ! ! interface 'Loopback .*' address-family ipv4 unicast ! ! ! end-group ! interface Loopback0 ipv4 address 4.4.4.4 255.255.255.255 ! interface GigabitEthernet0/0/0/0 ipv4 address 10.2.4.4 255.255.255.0 ! interface GigabitEthernet0/0/0/1 ipv4 address 10.4.5.4 255.255.255.0 ! interface GigabitEthernet0/0/0/2 ipv4 address 10.4.6.4 255.255.255.0 ! interface GigabitEthernet0/0/0/3 ipv4 address 10.3.4.4 255.255.255.0 ! router isis 1 apply-group CCIE-ISIS net 49.0001.0000.0000.0004.00 interface Loopback0 address-family ipv4 unicast prefix-sid index 4 ! ! interface GigabitEthernet0/0/0/0 address-family ipv4 unicast metric 1000 ! ! interface GigabitEthernet0/0/0/1 ! interface GigabitEthernet0/0/0/2 address-family ipv4 unicast metric 1000 ! ! interface GigabitEthernet0/0/0/3 ! ! mpls oam ! end
h_N5
hostname h_N5 group CCIE-ISIS router isis '.*' is-type level-2-only address-family ipv4 unicast metric-style wide segment-routing mpls ! interface 'Gi.*' point-to-point address-family ipv4 unicast ! ! interface 'Loopback .*' address-family ipv4 unicast ! ! ! end-group ! interface Loopback0 ipv4 address 5.5.5.5 255.255.255.255 ! interface GigabitEthernet0/0/0/0 ipv4 address 10.3.5.5 255.255.255.0 ! interface GigabitEthernet0/0/0/1 ipv4 address 10.4.5.5 255.255.255.0 ! interface GigabitEthernet0/0/0/2 ipv4 address 10.5.6.5 255.255.255.0 ! ! router isis 1 apply-group CCIE-ISIS net 49.0001.0000.0000.0005.00 interface Loopback0 address-family ipv4 unicast prefix-sid index 5 ! ! interface GigabitEthernet0/0/0/0 address-family ipv4 unicast metric 1000 ! ! interface GigabitEthernet0/0/0/1 ! interface GigabitEthernet0/0/0/2 ! ! mpls oam ! end
h_N6
hostname h_N6 group CCIE-ISIS router isis '.*' is-type level-2-only address-family ipv4 unicast metric-style wide segment-routing mpls ! interface 'Gi.*' point-to-point address-family ipv4 unicast ! ! interface 'Loopback .*' address-family ipv4 unicast ! ! ! end-group ! interface Loopback0 ipv4 address 6.6.6.6 255.255.255.255 ! interface GigabitEthernet0/0/0/0 ipv4 address 10.4.6.6 255.255.255.0 ! interface GigabitEthernet0/0/0/2 ipv4 address 10.5.6.6 255.255.255.0 ! router isis 1 apply-group CCIE-ISIS net 49.0001.0000.0000.0006.00 interface Loopback0 address-family ipv4 unicast prefix-sid index 6 ! ! interface GigabitEthernet0/0/0/0 address-family ipv4 unicast metric 1000 ! ! interface GigabitEthernet0/0/0/2 ! ! mpls oam ! end
4．実装
実装の流れは、①全ノードでSegment Routing を有効にしてから ②Head-End で explicit Path を定義し、 ③SR-TEのポリシーを定義します。④最後に経路の候補(Candidate-paths)を②で指定した path list から選択します。
4.1 全ノード共通
IGPでSegment Routing を有効にします。 segment-routing mpls （忘れずに Loopback0 で prefix-sid index X を有効化します）
router isis '.*'
net 49.0001.0000.0000.000X.00
address-family ipv4 unicast
metric-style wide
segment-routing mpls
!
interface Loopback 0
address-family ipv4 unicast
prefix-sid index X
!
!
!
4.2 SR-TEの実装とは無関係のネタ仕込み
ノード h_N2 でSRLBを定義します。rangeは、24000-25000とします。
RP/0/RP0/CPU0:h_N2(config)#segment-routing RP/0/RP0/CPU0:h_N2(config-sr)#local-block 24000 25000 RP/0/RP0/CPU0:h_N2(config-sr)#commit Sun Mar 12 14:03:29.916 UTC RP/0/RP0/CPU0:Mar 12 14:03:32.614 UTC: mpls_lsd[187]: %ROUTING-MPLS_LSD-3-ERR_SRLB_RANGE : SRLB allocation failed: 'SRLB reservation not successfull for [24000,25000]. Use with caution 'clear segment-routing local-block discrepancy all' command to force srlb allocation' RP/0/RP0/CPU0:h_N2(config-sr)#
'clear segment-routing local-block discrepancy all' command を実行せよ！と言われます。
実行しないと．．．この通り
RP/0/RP0/CPU0:h_N2(config-sr)#do show mpls forwarding Sun Mar 12 14:03:39.538 UTC Local Outgoing Prefix Outgoing Next Hop Bytes Label Label or ID Interface Switched ------ ----------- ------------------ ------------ --------------- ------------ 16001 Pop SR Pfx (idx 1) Gi0/0/0/0 10.1.2.1 23836 16003 16003 SR Pfx (idx 3) Gi0/0/0/0 10.1.2.1 0 16004 16004 SR Pfx (idx 4) Gi0/0/0/0 10.1.2.1 2328 16005 16005 SR Pfx (idx 5) Gi0/0/0/0 10.1.2.1 0 16006 16006 SR Pfx (idx 6) Gi0/0/0/0 10.1.2.1 0 24000 Pop SR Adj (idx 1) Gi0/0/0/0 10.1.2.1 0 24001 Pop SR Adj (idx 3) Gi0/0/0/0 10.1.2.1 0 24004 Pop SR Adj (idx 1) Gi0/0/0/2 10.2.4.4 0 24005 Pop SR Adj (idx 3) Gi0/0/0/2 10.2.4.4 0 RP/0/RP0/CPU0:h_N2(config-sr)#
SRLBを再計算してくれません。言われた通りにコマンドを実行します。
do clear segment-routing local-block discrepancy all
暫くすると指定したSRLBを加味してLSDを再計算します。
RP/0/RP0/CPU0:h_N2(config-sr)#do show mpls forwarding Sun Mar 12 14:04:38.443 UTC Local Outgoing Prefix Outgoing Next Hop Bytes Label Label or ID Interface Switched ------ ----------- ------------------ ------------ --------------- ------------ 16001 Pop SR Pfx (idx 1) Gi0/0/0/0 10.1.2.1 23836 16003 16003 SR Pfx (idx 3) Gi0/0/0/0 10.1.2.1 0 16004 16004 SR Pfx (idx 4) Gi0/0/0/0 10.1.2.1 2328 16005 16005 SR Pfx (idx 5) Gi0/0/0/0 10.1.2.1 0 16006 16006 SR Pfx (idx 6) Gi0/0/0/0 10.1.2.1 0 ★25001 Pop SR Adj (idx 1) Gi0/0/0/0 10.1.2.1 0 ★25002 Pop SR Adj (idx 3) Gi0/0/0/0 10.1.2.1 0 ★25003 Pop SR Adj (idx 1) Gi0/0/0/2 10.2.4.4 0 ★25004 Pop SR Adj (idx 3) Gi0/0/0/2 10.2.4.4 0 RP/0/RP0/CPU0:h_N2(config-sr)#
★部の値がdefault値から変わったことにお気づきでしょうか。default の Dynamic Label range は24000からなのですが。 今SRLBを24000-25000としたがために Dynamic Label range が 25001～に変更されたのです。 ここで、h_N2 - h_N4 のリンクに明示的にAdj-SIDを定義します。
router isis 1 interface GigabitEthernet 0/0/0/2 address-family ipv4 unicast adjacency-sid index 365 protected adjacency-sid index 366 ! ! !
このAdj-SIDは通常のそれとは違い固定で割り当てられます。どういう使い道があるのかは別として複数定義することが可能です。 確認コマンドは以下の通りです。
RP/0/RP0/CPU0:h_N2#show isis segment-routing label adjacency persistent
Sun Mar 12 14:46:02.607 UTC
IS-IS 1 Manual Adjacency SID Table
24365 AF IPv4
GigabitEthernet0/0/0/2: IPv4, Protected 1/255/N, Active
24366 AF IPv4
GigabitEthernet0/0/0/2: IPv4, Not protected 1/255/N, Active
RP/0/RP0/CPU0:h_N2#
SRLB を定義したノード h_N2 の LFIB を見てみましょう。
RP/0/RP0/CPU0:h_N2#show mpls forwarding
Sun Mar 12 14:47:44.792 UTC
Local Outgoing Prefix Outgoing Next Hop Bytes
Label Label or ID Interface Switched
------ ----------- ------------------ ------------ --------------- ------------
16001 Pop SR Pfx (idx 1) Gi0/0/0/0 10.1.2.1 24364
16003 Pop SR Pfx (idx 3) Gi0/0/0/1 10.2.3.3 0
16004 16004 SR Pfx (idx 4) Gi0/0/0/1 10.2.3.3 0
16005 16005 SR Pfx (idx 5) Gi0/0/0/1 10.2.3.3 0
16006 16006 SR Pfx (idx 6) Gi0/0/0/1 10.2.3.3 0
★1 24365 Pop SRLB (idx 365) Gi0/0/0/2 10.2.4.4 0
★2 24366 Pop SRLB (idx 366) Gi0/0/0/2 10.2.4.4 0
25001 Pop SR Adj (idx 1) Gi0/0/0/0 10.1.2.1 0
25002 Pop SR Adj (idx 3) Gi0/0/0/0 10.1.2.1 0
★3 25003 Pop SR Adj (idx 1) Gi0/0/0/2 10.2.4.4 0
★4 25004 Pop SR Adj (idx 3) Gi0/0/0/2 10.2.4.4 0
25005 Pop SR Adj (idx 1) Gi0/0/0/1 10.2.3.3 0
25006 Pop SR Adj (idx 3) Gi0/0/0/1 10.2.3.3 0
RP/0/RP0/CPU0:h_N2#
★1-2 が persistence Adj-SIDs ※ SRLB が目印となります。
★3-4 がDynamic Adj-SIDs
4.3 Head-End(h_N1)
4.3.1 explicit Path の定義
① Segment Routing を定義します。
RP/0/RP0/CPU0:h_N1(config)#? segment-routing Segment Routing
② Segment Routing で Traffic Engineering を定義します。
RP/0/RP0/CPU0:h_N1(config-sr)#? traffic-eng Segment Routing Traffic Engineering
③ Segment-list configuration でSegment-list名(任意：EXPLICIT_LIST)を定義します。
RP/0/RP0/CPU0:h_N1(config-sr-te)#? segment-list Segment-list configuration RP/0/RP0/CPU0:h_N1(config-sr-te)#segment-list ? name Segment-list name WORD Identifying name for segment-list RP/0/RP0/CPU0:h_N1(config-sr-te)#segment-list EXPLICIT_LIST
④ SR-TEで経路を明示的に定義します。
RP/0/RP0/CPU0:h_N1(config-sr-te-sl)#? index Next entry index RP/0/RP0/CPU0:h_N1(config-sr-te-sl)#index ? <1-65535> Index number RP/0/RP0/CPU0:h_N1(config-sr-te-sl)#index 10 ? mpls MPLS configuration RP/0/RP0/CPU0:h_N1(config-sr-te-sl)#index 10 mpls ? label MPLS label configuration RP/0/RP0/CPU0:h_N1(config-sr-te-sl)#index 10 mpls label ? <0-1048575> MPLS label value RP/0/RP0/CPU0:h_N1(config-sr-te-sl)#index 10 mpls label 16003 ? <cr>
今回は、Node1→3→2→4→5→6 とします。
segment-routing traffic-eng segment-list EXPLICIT_LIST index 10 mpls label 16003 index 20 mpls label 16002 index 30 mpls label 24365 index 40 mpls label 16005 index 50 mpls label 16006 ! ! !
4.3.2 SR-TE Policy の定義
SR-TE Policy を以下のように定義します。
a) ポリシー名 ：EXPLICIT_PATH_POLICY
b) B-SID(任意)：24365
c) color ：6
d) Tail-End ：6.6.6.6(h_N6)
SR-TEは、a)ポリシー名とc)カラー、d)Tail-Endの指定が必須です。
① 先ずはポリシー名を定義します。
RP/0/RP0/CPU0:h_N1(config-sr-te)#policy ? WORD Identifying name for policy with max 59 characters RP/0/RP0/CPU0:h_N1(config-sr-te)#policy EXPLICIT_PATH_POLICY
② B-SID(binding-sid)は任意設定です。
※ SR-TE Policy自体に割り当てられたSIDをB-SID(binding-sid)と呼びます。
RP/0/RP0/CPU0:h_N1(config-sr-te-policy)#? binding-sid Binding Segment Identifier RP/0/RP0/CPU0:h_N1(config-sr-te-policy)#binding-sid ? mpls MPLS label RP/0/RP0/CPU0:h_N1(config-sr-te-policy)#binding-sid mpls ? <16-1048575> MPLS label RP/0/RP0/CPU0:h_N1(config-sr-te-policy)#binding-sid mpls 24365 ? <cr>
③ 次にカラーとTail-Endを指定します。
RP/0/RP0/CPU0:h_N1(config-sr-te-policy)#? color Specify color for policy RP/0/RP0/CPU0:h_N1(config-sr-te-policy)#color ? <1-4294967295> Color value RP/0/RP0/CPU0:h_N1(config-sr-te-policy)#color 6 ? end-point Policy endpoint RP/0/RP0/CPU0:h_N1(config-sr-te-policy)#color 6 end-point ? ipv4 IPv4 address RP/0/RP0/CPU0:h_N1(config-sr-te-policy)#color 6 end-point ipv4 ? A.B.C.D IPv4 endpoint address RP/0/RP0/CPU0:h_N1(config-sr-te-policy)#color 6 end-point ipv4 6.6.6.6 ? <cr>
④ SR-TEポリシーで作成したLSP経由でパケットを転送させるため、autorouteを定義します。
端的に言うと、For traffic steering toward h_N6 ってことです。
RP/0/RP0/CPU0:h_N1(config-sr-te-policy)#? autoroute Autoroute configuration RP/0/RP0/CPU0:h_N1(config-sr-te-policy)#autoroute RP/0/RP0/CPU0:h_N1(config-sr-te-policy-autoroute)#? include Prefixes for which IGP routes will be installed RP/0/RP0/CPU0:h_N1(config-sr-te-policy-autoroute)#include ? all Include all eligible prefixes ipv4 IPv4 address family RP/0/RP0/CPU0:h_N1(config-sr-te-policy-autoroute)#include ipv4 ? A.B.C.D/length IP prefix route to include RP/0/RP0/CPU0:h_N1(config-sr-te-policy-autoroute)#include ipv4 6.6.6.6/32
4.3.3 Candidate-paths の定義
Candidate-paths を以下のように定義します。
a) preference ：100(大きい方が優先されます！)
b) explicit path ：EXPLICIT_LIST
preference と指定する経路リストをセットで指定します。
RP/0/RP0/CPU0:h_N1(config-sr-te-policy)#? candidate-paths Candidate-paths configuration RP/0/RP0/CPU0:h_N1(config-sr-te-policy)#candidate-paths RP/0/RP0/CPU0:h_N1(config-sr-te-policy-path)#? preference Policy path-option preference entry RP/0/RP0/CPU0:h_N1(config-sr-te-policy-path)#preference ? <1-65535> Path-option preference RP/0/RP0/CPU0:h_N1(config-sr-te-policy-path)#preference 100 RP/0/RP0/CPU0:h_N1(config-sr-te-policy-path-pref)#? explicit Preconfigured path RP/0/RP0/CPU0:h_N1(config-sr-te-policy-path-pref)#explicit ? segment-list Specify Segment-list RP/0/RP0/CPU0:h_N1(config-sr-te-policy-path-pref)#explicit segment-list ? EXPLICIT_LIST Identifying name for segment-list WORD Identifying name for segment-list RP/0/RP0/CPU0:h_N1(config-sr-te-policy-path-pref)#explicit segment-list EXPLICIT_LIST
ここでpreferenceを比較するために、別の segment-list を定義しておきます。
※ ★の箇所です。
segment-routing
traffic-eng
segment-list EXPLICIT_LIST
index 10 mpls label 16003
index 20 mpls label 16002
index 30 mpls label 24365
index 40 mpls label 16005
index 50 mpls label 16006
!
★ segment-list PREF_75_EXPLICIT_LIST
★ index 10 mpls label 16003
★ index 20 mpls label 16005
★ index 30 mpls label 16006
!
policy EXPLICIT_PATH_POLICY
binding-sid mpls 24365
color 6 end-point ipv4 6.6.6.6
autoroute
include ipv4 6.6.6.6/32
!
candidate-paths
★ preference 75
★ explicit segment-list PREF_75_EXPLICIT_LIST
!
!
preference 100
explicit segment-list EXPLICIT_LIST
!
!
!
!
!
!
5. 検証
SR-TE(explicit path)を実装する前はこうでした。
RP/0/RP0/CPU0:h_N1#show route | begin Gate
Sun Mar 12 06:26:55.756 UTC
Gateway of last resort is not set
L 1.1.1.1/32 is directly connected, 5w2d, Loopback0
i L2 2.2.2.2/32 [115/20] via 10.1.2.2, 5w2d, GigabitEthernet0/0/0/0
i L2 3.3.3.3/32 [115/20] via 10.1.3.3, 02:00:01, GigabitEthernet0/0/0/2
i L2 4.4.4.4/32 [115/30] via 10.1.3.3, 01:45:48, GigabitEthernet0/0/0/2
i L2 5.5.5.5/32 [115/40] via 10.1.3.3, 01:45:48, GigabitEthernet0/0/0/2
i L2 6.6.6.6/32 [115/50] via 10.1.3.3, 01:45:20, GigabitEthernet0/0/0/2
C 10.1.2.0/24 is directly connected, 5w2d, GigabitEthernet0/0/0/0
L 10.1.2.1/32 is directly connected, 5w2d, GigabitEthernet0/0/0/0
C 10.1.3.0/24 is directly connected, 5w2d, GigabitEthernet0/0/0/2
L 10.1.3.1/32 is directly connected, 5w2d, GigabitEthernet0/0/0/2
i L2 10.2.3.0/24 [115/20] via 10.1.2.2, 01:48:33, GigabitEthernet0/0/0/0
[115/20] via 10.1.3.3, 01:48:33, GigabitEthernet0/0/0/2
i L2 10.2.4.0/24 [115/30] via 10.1.3.3, 01:45:48, GigabitEthernet0/0/0/2
i L2 10.3.4.0/24 [115/20] via 10.1.3.3, 02:00:01, GigabitEthernet0/0/0/2
i L2 10.3.5.0/24 [115/40] via 10.1.3.3, 01:45:48, GigabitEthernet0/0/0/2
i L2 10.4.5.0/24 [115/30] via 10.1.3.3, 01:45:48, GigabitEthernet0/0/0/2
i L2 10.4.6.0/24 [115/50] via 10.1.3.3, 01:45:20, GigabitEthernet0/0/0/2
i L2 10.5.6.0/24 [115/40] via 10.1.3.3, 01:45:20, GigabitEthernet0/0/0/2
L 127.0.0.0/8 [0/0] via 0.0.0.0, 5w2d
RP/0/RP0/CPU0:h_N1#
RP/0/RP0/CPU0:h_N1#show ip interface brief | exclude una
Sun Mar 12 06:27:17.857 UTC
Interface IP-Address Status Protocol Vrf-Name
Loopback0 1.1.1.1 Up Up default
GigabitEthernet0/0/0/0 10.1.2.1 Up Up default
GigabitEthernet0/0/0/2 10.1.3.1 Up Up default
RP/0/RP0/CPU0:h_N1#
RP/0/RP0/CPU0:h_N1#traceroute 6.6.6.6 source 1.1.1.1
Sun Mar 12 06:27:50.065 UTC
Type escape sequence to abort.
Tracing the route to 6.6.6.6
1 10.1.3.3 [MPLS: Label 16006 Exp 0] 21 msec 4 msec 3 msec
2 10.3.4.4 [MPLS: Label 16006 Exp 0] 6 msec 3 msec 3 msec
3 10.4.5.5 [MPLS: Label 16006 Exp 0] 6 msec 4 msec 3 msec
4 10.5.6.6 9 msec * 6 msec
RP/0/RP0/CPU0:h_N1#
SR-TEを定義すると新しいインターフェース(SR-TE用のLSP)が出現します。
RP/0/RP0/CPU0:h_N1#show ip interface brief | exclude una Sun Mar 12 08:21:57.825 UTC Interface IP-Address Status Protocol Vrf-Name ★srte_c_6_ep_6.6.6.6 1.1.1.1 Up Up default Loopback0 1.1.1.1 Up Up default GigabitEthernet0/0/0/0 10.1.2.1 Up Up default GigabitEthernet0/0/0/2 10.1.3.1 Up Up default RP/0/RP0/CPU0:h_N1#
今回定義したSR-TEポリシーは、Head-End：1.1.1.1(h_N1)、color：6、Tail-End：6.6.6.6(h_N6)です。 ルーティングテーブルにその変化が現れています。
RP/0/RP0/CPU0:h_N1#show route | begin Gate
Sun Mar 12 08:24:22.206 UTC
Gateway of last resort is not set
L 1.1.1.1/32 is directly connected, 5w2d, Loopback0
i L2 2.2.2.2/32 [115/20] via 10.1.2.2, 5w2d, GigabitEthernet0/0/0/0
i L2 3.3.3.3/32 [115/20] via 10.1.3.3, 03:57:27, GigabitEthernet0/0/0/2
i L2 4.4.4.4/32 [115/30] via 10.1.3.3, 03:43:15, GigabitEthernet0/0/0/2
i L2 5.5.5.5/32 [115/40] via 10.1.3.3, 03:43:15, GigabitEthernet0/0/0/2
★i L2 6.6.6.6/32 [115/50] via 6.6.6.6, 00:20:26, srte_c_6_ep_6.6.6.6
C 10.1.2.0/24 is directly connected, 5w2d, GigabitEthernet0/0/0/0
L 10.1.2.1/32 is directly connected, 5w2d, GigabitEthernet0/0/0/0
C 10.1.3.0/24 is directly connected, 5w2d, GigabitEthernet0/0/0/2
L 10.1.3.1/32 is directly connected, 5w2d, GigabitEthernet0/0/0/2
i L2 10.2.3.0/24 [115/20] via 10.1.2.2, 03:45:59, GigabitEthernet0/0/0/0
[115/20] via 10.1.3.3, 03:45:59, GigabitEthernet0/0/0/2
i L2 10.2.4.0/24 [115/30] via 10.1.3.3, 03:43:15, GigabitEthernet0/0/0/2
i L2 10.3.4.0/24 [115/20] via 10.1.3.3, 03:57:27, GigabitEthernet0/0/0/2
i L2 10.3.5.0/24 [115/40] via 10.1.3.3, 03:43:15, GigabitEthernet0/0/0/2
i L2 10.4.5.0/24 [115/30] via 10.1.3.3, 03:43:15, GigabitEthernet0/0/0/2
i L2 10.4.6.0/24 [115/50] via 10.1.3.3, 00:20:26, GigabitEthernet0/0/0/2
i L2 10.5.6.0/24 [115/40] via 10.1.3.3, 03:42:46, GigabitEthernet0/0/0/2
L 127.0.0.0/8 [0/0] via 0.0.0.0, 5w2d
RP/0/RP0/CPU0:h_N1#
Head-End：1.1.1.1(h_N1)の LFIB を確認すると、 SR-TEの NEXT_HOP やTail-End、B-SID(任意)：24365も確認できます。
SR-TE(EXPLICIT_PATH_POLICY)
・Head-End：1.1.1.1(h_N1)
・NEXT_HOP：10.1.3.3(Gi0/0/0/2)
・B-SID ：24365
RP/0/RP0/CPU0:h_N1#show mpls forwarding Sun Mar 12 15:37:01.656 UTC Local Outgoing Prefix Outgoing Next Hop Bytes Label Label or ID Interface Switched ------ ----------- ------------------ ------------ --------------- ------------ 16002 Pop SR Pfx (idx 2) Gi0/0/0/0 10.1.2.2 0 16003 Pop SR Pfx (idx 3) Gi0/0/0/2 10.1.3.3 0 16004 16004 SR Pfx (idx 4) Gi0/0/0/2 10.1.3.3 0 16005 16005 SR Pfx (idx 5) Gi0/0/0/2 10.1.3.3 0 16006 16006 SR Pfx (idx 6) Gi0/0/0/2 10.1.3.3 0 24000 Pop SR Adj (idx 1) Gi0/0/0/0 10.1.2.2 0 24001 Pop SR Adj (idx 3) Gi0/0/0/0 10.1.2.2 0 24002 Pop SR Adj (idx 1) Gi0/0/0/2 10.1.3.3 0 24003 Pop SR Adj (idx 3) Gi0/0/0/2 10.1.3.3 0 24004 Pop No ID Gi0/0/0/2 10.1.3.3 0 24005 16002 SR TE: 1 [TE-INT] Gi0/0/0/2 10.1.3.3 0 ★24006 Pop 6.6.6.6/32 srte_c_6_ep_ 6.6.6.6 0 ★24365 Pop No ID srte_c_6_ep_ point2point 0 RP/0/RP0/CPU0:h_N1#
CEFを確認するとSR-TEで定義した内容が反映されています。他のLoopbackアドレスと見比べると分かりやすいかと思います。
SR-TEのautorouteが効いています。他のLoopbackアドレスだとNEXT_HOPがインターフェース名ですが、Head-End宛だけがSR-TEになっています。
RP/0/RP0/CPU0:h_N1#show cef
Sun Mar 12 08:38:47.294 UTC
Prefix Next Hop Interface
------------------- ------------------- ------------------
0.0.0.0/0 drop default handler
0.0.0.0/32 broadcast
1.1.1.1/32 receive Loopback0
2.2.2.2/32 10.1.2.2/32 GigabitEthernet0/0/0/0
3.3.3.3/32 10.1.3.3/32 GigabitEthernet0/0/0/2
4.4.4.4/32 10.1.3.3/32 GigabitEthernet0/0/0/2
5.5.5.5/32 10.1.3.3/32 GigabitEthernet0/0/0/2
★6.6.6.6/32 6.6.6.6/32 srte_c_6_ep_6.6.6.6
10.1.2.0/24 attached GigabitEthernet0/0/0/0
10.1.2.0/32 broadcast GigabitEthernet0/0/0/0
10.1.2.1/32 receive GigabitEthernet0/0/0/0
10.1.2.255/32 broadcast GigabitEthernet0/0/0/0
10.1.3.0/24 attached GigabitEthernet0/0/0/2
10.1.3.0/32 broadcast GigabitEthernet0/0/0/2
10.1.3.1/32 receive GigabitEthernet0/0/0/2
10.1.3.255/32 broadcast GigabitEthernet0/0/0/2
10.2.3.0/24 10.1.2.2/32 GigabitEthernet0/0/0/0
10.1.3.3/32 GigabitEthernet0/0/0/2
10.2.4.0/24 10.1.3.3/32 GigabitEthernet0/0/0/2
10.3.4.0/24 10.1.3.3/32 GigabitEthernet0/0/0/2
10.3.5.0/24 10.1.3.3/32 GigabitEthernet0/0/0/2
10.4.5.0/24 10.1.3.3/32 GigabitEthernet0/0/0/2
10.4.6.0/24 10.1.3.3/32 GigabitEthernet0/0/0/2
10.5.6.0/24 10.1.3.3/32 GigabitEthernet0/0/0/2
127.0.0.0/8 receive
224.0.0.0/4 0.0.0.0/32
224.0.0.0/24 receive
255.255.255.255/32 broadcast
RP/0/RP0/CPU0:h_N1#
SR-TE ポリシーの情報はコマンドで確認することができます。
RP/0/RP0/CPU0:h_N1#show segment-routing traffic-eng policy
Sun Mar 12 08:48:06.458 UTC
SR-TE policy database
---------------------
Color: 6, End-point: 6.6.6.6
★1 Name: srte_c_6_ep_6.6.6.6
Status:
Admin: up Operational: up for 00:09:06 (since Mar 12 15:33:13.248)
Candidate-paths:
★2 Preference: 100 (configuration) (active)
Name: EXPLICIT_PATH_POLICY
Requested BSID: 24365
Protection Type: protected-preferred
Maximum SID Depth: 10
★3 Explicit: segment-list EXPLICIT_LIST (valid)
Weight: 1, Metric Type: TE
16003 [Prefix-SID, 3.3.3.3]
16002
24365
16005
16006
Preference: 75 (configuration)
Name: EXPLICIT_PATH_POLICY
Requested BSID: 24365
Protection Type: protected-preferred
Maximum SID Depth: 10
★4 Explicit: segment-list PREF_75_EXPLICIT_LIST (invalid)
Weight: 1, Metric Type: TE
Attributes:
★5 Binding SID: 24365
Forward Class: Not Configured
Steering labeled-services disabled: no
Steering BGP disabled: no
IPv6 caps enable: yes
Invalidation drop enabled: no
RP/0/RP0/CPU0:h_N1#
★1：Color と End-point(Head-End) が自動的にLSP名に反映されるのが特徴です。
SR-TE LSP名(Name: srte_c_6_ep_6.6.6.6)から、Color: 6, End-point: 6.6.6.6であることが分かります。
★2：Preference は大きい方が優先されます!
★3：有効な segment-list は、EXPLICIT_LIST (valid)です。
★4：Preference: 75 の segment-list である PREF_75_EXPLICIT_LIST (invalid) は無効になっています。
★5：このSR-TEに紐づけられているBinding SIDは、 24365 であることが分かります。
今回指定したBinding SIDを基にforwarding情報を確認すると似た内容を確認することができます。
RP/0/RP0/CPU0:h_N1#show segment-routing traffic-eng forwarding policy binding-sid 24365
Sun Mar 12 09:02:42.966 UTC
SR-TE Policy Forwarding database
--------------------------------
Color: 6, End-point: 6.6.6.6
★1 Name: srte_c_6_ep_6.6.6.6
★2 Binding SID: 24365
Active LSP:
★3 Candidate path:
Preference: 100 (configuration)
Name: EXPLICIT_PATH_POLICY
Local label: 24005
Segment lists:
SL[0]:
Name: EXPLICIT_LIST
Switched Packets/Bytes: 0/0
Paths:
Path[0]:
Outgoing Label: 16002
Outgoing Interfaces: GigabitEthernet0/0/0/2
★4 Next Hop: 10.1.3.3
Switched Packets/Bytes: 0/0
FRR Pure Backup: No
ECMP/LFA Backup: No
Internal Recursive Label: Unlabelled (recursive)
★5 Label Stack (Top -> Bottom): { 16002, 24365, 16005, 16006 }
Path-id: 1, Weight: 64
Policy Packets/Bytes Switched: 0/0
RP/0/RP0/CPU0:h_N1#
★1：Color と End-point(Head-End) が自動的にLSP名に反映されるのが特徴です。
SR-TE LSP名(Name: srte_c_6_ep_6.6.6.6)から、Color: 6, End-point: 6.6.6.6であることが分かります。
★2：このSR-TEに紐づけられているBinding SIDは、 24365 であることが分かります。
★3：今回選ばれた Preference は100で、有効な segment-list は、EXPLICIT_LIST (valid)です。
★4：NEXT_HOP は10.1.3.3（h_N3）です。
★5：segment-list は、EXPLICIT_LIST とおりに Label Stack していることが見て取れます。
疎通確認をすると想定通りの経路をたどっていることが分かります。
RP/0/RP0/CPU0:h_N1#traceroute 6.6.6.6 source loopback 0 Sun Mar 12 15:48:01.386 UTC Type escape sequence to abort. Tracing the route to 6.6.6.6 1 10.1.3.3 [MPLS: Labels 16002/24365/16005/16006 Exp 0] 51 msec 5 msec 3 msec 2 10.2.3.2 [MPLS: Labels 24365/16005/16006 Exp 0] 6 msec 5 msec 4 msec 3 10.2.4.4 [MPLS: Labels 16005/16006 Exp 0] 14 msec 4 msec 11 msec 4 10.4.5.5 [MPLS: Label 16006 Exp 0] 8 msec 3 msec 3 msec 5 10.5.6.6 13 msec * 6 msec RP/0/RP0/CPU0:h_N1#
6. SR-TE はいつダウンするのか
Head-End の冗長性を増強するため TI-LFA を設定します。
router isis 1 interface GigabitEthernet 0/0/0/0 point-to-point address-famili ipv4 unicast fast-reroute per-prefix fast-reroute per-prefix ti-lfa ! ! interface GigabitEthernet 0/0/0/2 point-to-point address-famili ipv4 unicast fast-reroute per-prefix fast-reroute per-prefix ti-lfa ! !
前半は先ほどのコマンドと同じですが、後半に Protected と Pure-Backup があることが分かります。
RP/0/RP0/CPU0:h_N1#show segment-routing traffic-eng forwarding policy detail
Sun Mar 12 15:50:42.782 UTC
SR-TE Policy Forwarding database
--------------------------------
Color: 6, End-point: 6.6.6.6
Name: srte_c_6_ep_6.6.6.6
Binding SID: 24365
Active LSP:
Candidate path:
Preference: 100 (configuration)
Name: EXPLICIT_PATH_POLICY
Local label: 24005
Segment lists:
SL[0]:
Name: EXPLICIT_LIST
Switched Packets/Bytes: 15/420
[MPLS -> MPLS]: 15/420
Paths:
Path[0]:
Outgoing Label: 16002
Outgoing Interfaces: GigabitEthernet0/0/0/2
Next Hop: 10.1.3.3
Switched Packets/Bytes: 15/420
[MPLS -> MPLS]: 15/420
FRR Pure Backup: No
ECMP/LFA Backup: No
Internal Recursive Label: Unlabelled (recursive)
Label Stack (Top -> Bottom): { 16002, 24365, 16005, 16006 }
Path-id: 1, Weight: 64
Reoptimized LSP:
Candidate path:
Preference: 100 (configuration)
Name: EXPLICIT_PATH_POLICY
Local label: 24008
Segment lists:
SL[0]:
Name: EXPLICIT_LIST
Switched Packets/Bytes: 0/0
Paths:
Path[0]:
★1 Outgoing Label: 16003
★2 Outgoing Interfaces: GigabitEthernet0/0/0/0
★3 Next Hop: 10.1.2.2
Switched Packets/Bytes: 0/0
FRR Pure Backup: Yes
ECMP/LFA Backup: Yes
Internal Recursive Label: Unlabelled (recursive)
★4 Label Stack (Top -> Bottom): { 16003, 16002, 24365, 16005, 16006 }
★5 Path-id: 1 (Pure-Backup), Weight: 64
Path[1]:
★6 Outgoing Label: 16002
★7 Outgoing Interfaces: GigabitEthernet0/0/0/2
★8 Next Hop: 10.1.3.3
Switched Packets/Bytes: 0/0
FRR Pure Backup: No
ECMP/LFA Backup: No
Internal Recursive Label: Unlabelled (recursive)
★9 Label Stack (Top -> Bottom): { 16002, 24365, 16005, 16006 }
★10 Path-id: 2 (Protected), Backup-path-id: 1, Weight: 64
Policy Packets/Bytes Switched: 15/420
RP/0/RP0/CPU0:h_N1#
★1-5 Backup経路情報
★1: Outgoing Label: 16003
★2: Outgoing Interfaces: GigabitEthernet0/0/0/0
★3: Next Hop: 10.1.2.2
★4: Label Stack (Top -> Bottom): { 16003, 16002, 24365, 16005, 16006 }
★5: Path-id: 1 (Pure-Backup), Weight: 64
★6-10 SR-TE(Protected)経路情報
★6: Outgoing Label: 16002
★7: Outgoing Interfaces: GigabitEthernet0/0/0/2
★8: Next Hop: 10.1.3.3
★9: Label Stack (Top -> Bottom): { 16002, 24365, 16005, 16006 }
★10: Path-id: 2 (Protected), Backup-path-id: 1, Weight: 64
TI-LFA を実装したことによる効果はグンバツです！
RP/0/RP0/CPU0:h_N1#show isis fast-reroute summary
Sat Mar 18 21:48:41.838 UTC
IS-IS 1 IPv4 Unicast FRR summary
Critical High Medium Low Total
Priority Priority Priority Priority
Prefixes reachable in L2
All paths protected 0 0 4 7 11
Some paths protected 0 0 0 0 0
Unprotected 0 0 1 0 1
Protection coverage 0.00% 0.00% 80.00% 100.00% 91.67%
RP/0/RP0/CPU0:h_N1#
ここで、h_N2－h_N4間のリンクを切断します。
TI-LFA が有効化されているのに迂回されません。
RP/0/RP0/CPU0:h_N1#traceroute 6.6.6.6 source 1.1.1.1 Sat Mar 18 04:05:10.898 UTC Type escape sequence to abort. Tracing the route to 6.6.6.6 1 * * * 2 * * * 3 * * * 4 * * * 5 * * * 6 * * * 7 * * * 8 * * * 9 * * * 10 * * * 11 * * * 12 * * * 13 * * * 14 * * * 15 * * * 16 * * * 17 * * * 18 * * * 19 * * * 20 * * * 21 * * * 22 * * * 23 * * * 24 * * * 25 * * * 26 * * * 27 * * * 28 * * * 29 * * * 30 * * * RP/0/RP0/CPU0:h_N1#
これは、Explicit Path で指定した persistence Adj-SIDs に原因があります。
Explicit Path の一部で persistence Adj-SIDs（SRLBを使ってstaticにAdj-SID）を指定しているため迂回することができなくなります。
∵ persistence Adj-SIDs：24365 を使って h_N2 から h_N4 に到達することは、リンクダウンしているインターフェース以外に存在しないためです。
これは、h_N2、h_N4、h_N5、h_N6 の Loopback0 が shutdown されても同様なことが言えます。
しかし、SR-TE は up/up（Admin: up Operational: up） の状態を維持します。
RP/0/RP0/CPU0:h_N1#show segment-routing traffic-eng policy
Sat Mar 18 04:31:59.187 UTC
SR-TE policy database
---------------------
Color: 6, End-point: 6.6.6.6
Name: srte_c_6_ep_6.6.6.6
Status:
★ Admin: up Operational: up for 5d12h (since Mar 12 15:33:13.248)
Candidate-paths:
Preference: 100 (configuration) (active)
Name: EXPLICIT_PATH_POLICY
Requested BSID: 24365
Protection Type: protected-preferred
Maximum SID Depth: 10
☆ Explicit: segment-list EXPLICIT_LIST (valid)
Weight: 1, Metric Type: TE
16003 [Prefix-SID, 3.3.3.3]
16002
24365
16005
16006
Preference: 75 (configuration)
Name: EXPLICIT_PATH_POLICY
Requested BSID: 24365
Protection Type: protected-preferred
Maximum SID Depth: 10
Explicit: segment-list PREF_75_EXPLICIT_LIST (invalid)
Weight: 1, Metric Type: TE
Attributes:
Binding SID: 24365
Forward Class: Not Configured
Steering labeled-services disabled: no
Steering BGP disabled: no
IPv6 caps enable: yes
Invalidation drop enabled: no
RP/0/RP0/CPU0:h_N1#
ここで、h_N2－h_N4間のリンクを元に戻します。
では、どのような時にSR-TEはDownするのでしょうか。
答えは、Explicit Path の最初の SID が Down している時のようです。h_N3 の Loopback0 を shutdown します。
RP/0/RP0/CPU0:h_N3#conf Sat Mar 18 05:06:21.651 UTC RP/0/RP0/CPU0:h_N3(config)#interface loopback 0 RP/0/RP0/CPU0:h_N3(config-if)#shutdown RP/0/RP0/CPU0:h_N3(config-if)#commit Sat Mar 18 05:06:31.329 UTC RP/0/RP0/CPU0:h_N3(config-if)#
Head-End（h_N1）で SR-TE の状態を確認してみます。
RP/0/RP0/CPU0:h_N1#show segment-routing traffic-eng policy
Sat Mar 18 05:08:17.818 UTC
SR-TE policy database
---------------------
Color: 6, End-point: 6.6.6.6
Name: srte_c_6_ep_6.6.6.6
Status:
★ Admin: up Operational: down for 00:01:46 (since Mar 18 05:06:31.812)
Candidate-paths:
Preference: 100 (configuration)
Name: EXPLICIT_PATH_POLICY
Requested BSID: 24365
Protection Type: protected-preferred
Maximum SID Depth: 10
☆ Explicit: segment-list EXPLICIT_LIST (invalid)
Last error: unresolved first label (16003)
Weight: 1, Metric Type: TE
Preference: 75 (configuration)
Name: EXPLICIT_PATH_POLICY
Requested BSID: 24365
Protection Type: protected-preferred
Maximum SID Depth: 10
☆ Explicit: segment-list PREF_75_EXPLICIT_LIST (invalid)
Last error: unresolved first label (16003)
Weight: 1, Metric Type: TE
Attributes:
Forward Class: 0
Steering labeled-services disabled: no
Steering BGP disabled: no
IPv6 caps enable: no
Invalidation drop enabled: no
RP/0/RP0/CPU0:h_N1#
SR-TE が Operational: down になっているため、ルーティングテーブルにも表示しなくなります。
RP/0/RP0/CPU0:h_N1#show route | b Gate
Sat Mar 18 05:44:34.905 UTC
Gateway of last resort is not set
L 1.1.1.1/32 is directly connected, 00:57:17, Loopback0
i L2 2.2.2.2/32 [115/20] via 10.1.2.2, 5d13h, GigabitEthernet0/0/0/0
[115/30] via 10.1.3.3, 5d13h, GigabitEthernet0/0/0/2 (!)
i L2 4.4.4.4/32 [115/40] via 10.1.2.2, 5d13h, GigabitEthernet0/0/0/0 (!)
[115/30] via 10.1.3.3, 5d13h, GigabitEthernet0/0/0/2
i L2 5.5.5.5/32 [115/50] via 10.1.2.2, 00:59:55, GigabitEthernet0/0/0/0 (!)
[115/40] via 10.1.3.3, 00:59:55, GigabitEthernet0/0/0/2
i L2 6.6.6.6/32 [115/60] via 10.1.2.2, 00:38:02, GigabitEthernet0/0/0/0 (!)
[115/50] via 10.1.3.3, 00:38:02, GigabitEthernet0/0/0/2
C 10.1.2.0/24 is directly connected, 5d14h, GigabitEthernet0/0/0/0
L 10.1.2.1/32 is directly connected, 5d14h, GigabitEthernet0/0/0/0
C 10.1.3.0/24 is directly connected, 5d14h, GigabitEthernet0/0/0/2
L 10.1.3.1/32 is directly connected, 5d14h, GigabitEthernet0/0/0/2
i L2 10.2.3.0/24 [115/20] via 10.1.2.2, 00:38:02, GigabitEthernet0/0/0/0
[115/20] via 10.1.3.3, 00:38:02, GigabitEthernet0/0/0/2
i L2 10.2.4.0/24 [115/40] via 10.1.2.2, 5d13h, GigabitEthernet0/0/0/0 (!)
[115/30] via 10.1.3.3, 5d13h, GigabitEthernet0/0/0/2
i L2 10.3.4.0/24 [115/30] via 10.1.2.2, 00:38:02, GigabitEthernet0/0/0/0 (!)
[115/20] via 10.1.3.3, 00:38:02, GigabitEthernet0/0/0/2
i L2 10.3.5.0/24 [115/50] via 10.1.2.2, 00:59:55, GigabitEthernet0/0/0/0 (!)
[115/40] via 10.1.3.3, 00:59:55, GigabitEthernet0/0/0/2
i L2 10.4.5.0/24 [115/40] via 10.1.2.2, 5d13h, GigabitEthernet0/0/0/0 (!)
[115/30] via 10.1.3.3, 5d13h, GigabitEthernet0/0/0/2
i L2 10.4.6.0/24 [115/60] via 10.1.2.2, 00:38:02, GigabitEthernet0/0/0/0 (!)
[115/50] via 10.1.3.3, 00:38:02, GigabitEthernet0/0/0/2
i L2 10.5.6.0/24 [115/50] via 10.1.2.2, 00:59:55, GigabitEthernet0/0/0/0 (!)
[115/40] via 10.1.3.3, 00:59:55, GigabitEthernet0/0/0/2
L 127.0.0.0/8 [0/0] via 0.0.0.0, 5d14h
RP/0/RP0/CPU0:h_N1#
インターフェースもダウンしていることが分かります。
RP/0/RP0/CPU0:h_N1#show ip interface brief | exclude una Sat Mar 18 05:46:39.979 UTC Interface IP-Address Status Protocol Vrf-Name srte_c_6_ep_6.6.6.6 1.1.1.1 Down Down default Loopback0 1.1.1.1 Up Up default GigabitEthernet0/0/0/0 10.1.2.1 Up Up default GigabitEthernet0/0/0/2 10.1.3.1 Up Up default RP/0/RP0/CPU0:h_N1#
SR-TE が Operational: down となると、トラフィックは当然意図した通りに流れなくなります。
h_N3's loopback0 shutdown（ when segment list of first prefix-SID DOWN）
RP/0/RP0/CPU0:h_N1#traceroute 6.6.6.6 source 1.1.1.1 Sat Mar 18 05:11:29.211 UTC Type escape sequence to abort. Tracing the route to 6.6.6.6 1 10.1.3.3 [MPLS: Label 16006 Exp 0] 12 msec 5 msec 4 msec 2 10.3.4.4 [MPLS: Label 16006 Exp 0] 7 msec 4 msec 5 msec 3 10.4.5.5 [MPLS: Label 16006 Exp 0] 8 msec 4 msec 4 msec 4 10.5.6.6 11 msec * 7 msec RP/0/RP0/CPU0:h_N1#
最後に、Head-End（h_N1）の Loopback0 を shutdown するとどうなるかを示して終わります。
RP/0/RP0/CPU0:h_N1#show ip interface brief | exclude una
Sat Mar 18 21:08:32.349 UTC
Interface IP-Address Status Protocol Vrf-Name
Loopback0 1.1.1.1 Shutdown Down default
GigabitEthernet0/0/0/0 10.1.2.1 Up Up default
GigabitEthernet0/0/0/2 10.1.3.1 Up Up default
RP/0/RP0/CPU0:h_N1#
RP/0/RP0/CPU0:h_N1#show route | begin Gate
Sat Mar 18 21:08:58.024 UTC
Gateway of last resort is not set
i L2 2.2.2.2/32 [115/20] via 10.1.2.2, 6d05h, GigabitEthernet0/0/0/0
[115/30] via 10.1.3.3, 6d05h, GigabitEthernet0/0/0/2 (!)
i L2 3.3.3.3/32 [115/30] via 10.1.2.2, 09:13:25, GigabitEthernet0/0/0/0 (!)
[115/20] via 10.1.3.3, 09:13:25, GigabitEthernet0/0/0/2
i L2 4.4.4.4/32 [115/40] via 10.1.2.2, 6d05h, GigabitEthernet0/0/0/0 (!)
[115/30] via 10.1.3.3, 6d05h, GigabitEthernet0/0/0/2
i L2 5.5.5.5/32 [115/50] via 10.1.2.2, 00:43:32, GigabitEthernet0/0/0/0 (!)
[115/40] via 10.1.3.3, 00:43:32, GigabitEthernet0/0/0/2
i L2 6.6.6.6/32 [115/60] via 10.1.2.2, 00:43:15, GigabitEthernet0/0/0/0 (!)
[115/50] via 10.1.3.3, 00:43:15, GigabitEthernet0/0/0/2
C 10.1.2.0/24 is directly connected, 6d05h, GigabitEthernet0/0/0/0
L 10.1.2.1/32 is directly connected, 6d05h, GigabitEthernet0/0/0/0
C 10.1.3.0/24 is directly connected, 6d05h, GigabitEthernet0/0/0/2
L 10.1.3.1/32 is directly connected, 6d05h, GigabitEthernet0/0/0/2
i L2 10.2.3.0/24 [115/20] via 10.1.2.2, 09:13:25, GigabitEthernet0/0/0/0
[115/20] via 10.1.3.3, 09:13:25, GigabitEthernet0/0/0/2
i L2 10.2.4.0/24 [115/40] via 10.1.2.2, 6d05h, GigabitEthernet0/0/0/0 (!)
[115/30] via 10.1.3.3, 6d05h, GigabitEthernet0/0/0/2
i L2 10.3.4.0/24 [115/30] via 10.1.2.2, 09:13:25, GigabitEthernet0/0/0/0 (!)
[115/20] via 10.1.3.3, 09:13:25, GigabitEthernet0/0/0/2
i L2 10.3.5.0/24 [115/50] via 10.1.2.2, 00:43:32, GigabitEthernet0/0/0/0 (!)
[115/40] via 10.1.3.3, 00:43:32, GigabitEthernet0/0/0/2
i L2 10.4.5.0/24 [115/40] via 10.1.2.2, 6d05h, GigabitEthernet0/0/0/0 (!)
[115/30] via 10.1.3.3, 6d05h, GigabitEthernet0/0/0/2
i L2 10.4.6.0/24 [115/60] via 10.1.2.2, 00:43:15, GigabitEthernet0/0/0/0 (!)
[115/50] via 10.1.3.3, 00:43:15, GigabitEthernet0/0/0/2
i L2 10.5.6.0/24 [115/50] via 10.1.2.2, 00:43:32, GigabitEthernet0/0/0/0 (!)
[115/40] via 10.1.3.3, 00:43:32, GigabitEthernet0/0/0/2
L 127.0.0.0/8 [0/0] via 0.0.0.0, 6d05h
RP/0/RP0/CPU0:h_N1#
RP/0/RP0/CPU0:h_N1#show segment-routing traffic-eng policy
Sat Mar 18 21:09:12.783 UTC
SR-TE policy database
---------------------
Color: 6, End-point: 6.6.6.6
Name: srte_c_6_ep_6.6.6.6
Status:
★ Admin: up Operational: down for 00:43:30 (since Mar 18 20:25:42.419)
Candidate-paths:
Preference: 100 (configuration)
Name: EXPLICIT_PATH_POLICY
Requested BSID: 24365
Protection Type: protected-preferred
Maximum SID Depth: 10
☆ Explicit: segment-list EXPLICIT_LIST (invalid)
Weight: 1, Metric Type: TE
Preference: 75 (configuration)
Name: EXPLICIT_PATH_POLICY
Requested BSID: 24365
Protection Type: protected-preferred
Maximum SID Depth: 10
☆ Explicit: segment-list PREF_75_EXPLICIT_LIST (invalid)
Last error: unresolved first label (16003)
Weight: 1, Metric Type: TE
Attributes:
Forward Class: 0
Steering labeled-services disabled: no
Steering BGP disabled: no
IPv6 caps enable: no
Invalidation drop enabled: no
RP/0/RP0/CPU0:h_N1#
当然のことながら、SR-TE が Operational: down となり、トラフィックも流れません。
7. 参考
① Configure SR-TE Policy with Explicit Path www.cisco.com
② Segment Routing Traffic Engineering – Explicit Candidate Path y-network.jp
次回は、WECMP（重みづけ等コストロードバランシング）について記事を書きます。
最後までお読みいただきありがとうございました！
