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Cisco Bug: CSCup90279 - SR: SID misconfig in different IGPs result in route inconsistency

Last Modified

Jan 11, 2017

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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