Cisco Bug: CSCup90279 - SR: SID misconfig in different IGPs result in route inconsistency
Last Modified
Jun 08, 2018
Products (1)
- Cisco Carrier Routing System
Known Affected Releases
5.2.2.BASE
Description (partial)
Symptom: Sympton 1: label recycle complain from FIB ---------------------------------------------- 1. Because OSPF has lower admin distance, RIB will download the OSPF prefix. 2. First FIB will reject the route update LC/0/3/CPU0:Jul 16 16:50:43.697 : fib_mgr[159]: %ROUTING-FIB-5-ROUTE_UPDATE_DROP : FIB dropping route update: LABEL-RECYCLING: label=43001 new-prefix=3.0.0.2/32, tbl=default, old-prefix=3.0.0.1/32, tbl=default, rt-src=7 LC/0/2/CPU0:Jul 16 16:50:43.698 : fib_mgr[159]: %ROUTING-FIB-5-ROUTE_UPDATE_DROP : FIB dropping route update: LABEL-RECYCLING: label=43001 new-prefix=3.0.0.2/32, tbl=default, old-prefix=3.0.0.1/32, tbl=default, rt-src=7 RP/0/0/CPU0:Jul 16 16:50:43.697 : fib_mgr[210]: %ROUTING-FIB-5-ROUTE_UPDATE_DROP : FIB dropping route update: LABEL-RECYCLING: label=43001 new-prefix=3.0.0.2/32, tbl=default, old-prefix=3.0.0.1/32, tbl=default, rt-src=7 LC/0/1/CPU0:Jul 16 16:50:43.703 : fib_mgr[158]: %ROUTING-FIB-5-ROUTE_UPDATE_DROP : FIB dropping route update: LABEL-RECYCLING: label=43001 new-prefix=3.0.0.2/32, tbl=default, old-prefix=3.0.0.1/32, tbl=default, rt-src=7 Sympton 2: route inconsistency ------------------------------- RP/0/0/CPU0:pallas-R4#show route 3.0.0.2 det Wed Jul 16 17:01:08.835 UTC Routing entry for 3.0.0.2/32 Known via "ospf 100", distance 110, metric 2, type intra area Installed Jul 16 16:50:43.690 for 00:10:25 Routing Descriptor Blocks 100.1.1.3, from 3.0.0.1, via GigabitEthernet0/1/0/1 Route metric is 2 Label: 0x3 (3) Tunnel ID: None Extended communities count: 0 Path id:1 Path ref count:0 NHID:0x0(Ref:0) OSPF area: 0 Route version is 0xf (15) Local Label: 0xa7f9 (43001) <<<<<<<<<<<<<<<<<<<<<<<<<<<< IP Precedence: Not Set QoS Group ID: Not Set Flow-tag: Not Set Route Priority: RIB_PRIORITY_NON_RECURSIVE_MEDIUM (7) SVD Type RIB_SVD_TYPE_LOCAL Download Priority 1, Download Version 393623 No advertising protos. RP/0/0/CPU0:pallas-R4#show cef 3.0.0.2 Wed Jul 16 17:01:15.106 UTC 3.0.0.2/32, version 393621, internal 0x2000001 0x1 (ptr 0xaf3775ec) [1], 0x0 (0xaea53c80), 0xa20 (0xaecf3270) Updated Jul 16 16:47:53.628 local adjacency 100.1.1.3 Prefix Len 32, traffic index 0, precedence n/a, priority 1 via 100.1.1.3, GigabitEthernet0/1/0/1, 11 dependencies, weight 0, class 0 [flags 0x0] path-idx 0 NHID 0x0 [0xaefdf18c 0x0] next hop 100.1.1.3 tx adjacency labels imposed {None} <<<<<<<<<<<<<<<<<<<<<<<<<<< As we can see, FIB still has the ISIS route which had no labels while RIB has the OSPF route which had a label Symton 3: No recovery after ISIS withdraws the route ---------------------------------------------------- Even after ISIS withdraws the prefix offending prefix 3.0.0.1 which had the prefix-SID 3001, FIB will NOT have the prefix 3.0.0.2 because FIB rejected the router update due to label conflict RP/0/0/CPU0:pallas-R4#show isis route 3.0.0.1/32 Wed Jul 16 17:17:33.888 UTC The requested route 3.0.0.1/32 was not found in the IS-IS 1 IPv4 Unicast Route Table RP/0/0/CPU0:pallas-R4# RP/0/0/CPU0:pallas-R4#show cef 3.0.0.2 Wed Jul 16 17:18:01.502 UTC 0.0.0.0/0, version 0, proxy default, default route handler, drop adjacency, internal 0x2002021 0x0 (ptr 0xaeab706c) [1], 0x0 (0xaea53050), 0x0 (0x0) Updated Jul 9 20:18:19.897 Prefix Len 0, traffic index 0, precedence n/a, priority 15 via point2point, 3 dependencies, weight 0, class 0 [flags 0x0] path-idx 0 NHID 0x0 [0xadfe73d4 0x0] next hop point2point drop adjacency RP/0/0/CPU0:pallas-R4# Conditions: All of the following conditions MUST be satisifed - A router R1 running both OSPF and ISIS or different instances of OSPF or different instances of ISIS - A remote router "R2" running OSPF advertises prefix-SID "S" for the prefix "P1" - The same or another router "R3" running ISIS advertises the same prefix-SID "S" but for a different prefix "P2" - the router "R1" receives the ISIS advertisement first and downloads that prefix with its corresponding label to RIB and FIB - The router "R1" receives the OSPF advertisement after that such that the SID "S" results in the same label used for prefix "P2"
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