Hello Con,
I was able to reproduce the problem:
++++++++++++++++++++++++++++
R1#sh ip route vrf VPNB 8.8.8.8
Routing entry for 8.8.8.8/32
Known via "bgp 125", distance 200, metric 0
Tag 678, type internal
Redistributing via ospf 39
Advertised by ospf 39 subnets
Last update from 6.7.8.8 00:00:23 ago
Routing Descriptor Blocks:
* 6.7.8.8 (Default-IP-Routing-Table), from 125.125.125.2, 00:00:23 ago
Route metric is 0, traffic share count is 1
AS Hops 1
Route tag 678
MPLS Required
R1#
01:04:03: %OSPF-5-ADJCHG: Process 39, Nbr 8.8.8.8 on OSPF_SL0 from FULL to
DOWN, Neighbor Down: Interface down or detached
R1#
R1#sh ip route vrf VPNB 8.8.8.8
Routing entry for 8.8.8.8/32
Known via "ospf 39", distance 110, metric 1
Tag Complete, Path Length == 1, AS 678, , type extern 2, forward metric 1
Redistributing via bgp 125
Last update from 6.7.8.8 00:00:05 ago
Routing Descriptor Blocks:
* 6.7.8.8 (Default-IP-Routing-Table), from 8.8.8.8, 00:00:05 ago
Route metric is 1, traffic share count is 1
Route tag 3489661606
R1#
R1#
01:04:16: %OSPF-5-ADJCHG: Process 39, Nbr 8.8.8.8 on OSPF_SL0 from LOADING to
FULL, Loading Done
R1#
R1#sh ip route vrf VPNB 8.8.8.8
Routing entry for 8.8.8.8/32
Known via "bgp 125", distance 200, metric 0
Tag 678, type internal
Redistributing via ospf 39
Advertised by ospf 39 subnets
Last update from 6.7.8.8 00:00:11 ago
Routing Descriptor Blocks:
* 6.7.8.8 (Default-IP-Routing-Table), from 125.125.125.2, 00:00:11 ago
Route metric is 0, traffic share count is 1
AS Hops 1
Route tag 678
MPLS Required
R1#
++++++++++++++++++++++++++++
The link between R3 and R9 is shutdown.
I am using 12.2(25)S13 in all routers in this lab.
The relevant configs:
R1:
!
interface Loopback1000
ip vrf forwarding VPNB
ip address 1.1.1.1 255.255.255.255
no clns route-cache
!
router ospf 39 vrf VPNB
log-adjacency-changes
area 0 sham-link 1.1.1.1 8.8.8.8
redistribute bgp 125 subnets
network 31.3.1.1 0.0.0.0 area 0
!
router bgp 125
bgp router-id 125.125.125.1
bgp always-compare-med
no bgp default ipv4-unicast
bgp log-neighbor-changes
neighbor 125.8.1.8 remote-as 678
neighbor 125.125.125.2 remote-as 125
neighbor 125.125.125.2 update-source Loopback0
neighbor 125.125.125.5 remote-as 125
neighbor 125.125.125.5 update-source Loopback0
!
address-family ipv4 vrf VPNB
redistribute connected
redistribute ospf 39 vrf VPNB match internal external 1 external 2 route-map
ospf2bgp
no auto-summary
no synchronization
exit-address-family
!
route-map ospf2bgp permit 10
set origin egp 1
!
R8:
!
interface Loopback1000
ip vrf forwarding VPNB
ip address 8.8.8.8 255.255.255.255
no clns route-cache
!
!
router ospf 39 vrf VPNB
log-adjacency-changes
area 0 sham-link 8.8.8.8 1.1.1.1
redistribute bgp 678 subnets
network 98.9.8.8 0.0.0.0 area 0
!
router bgp 678
bgp router-id 6.7.8.8
bgp always-compare-med
no bgp default ipv4-unicast
bgp log-neighbor-changes
neighbor as678 peer-group
neighbor as678 remote-as 678
neighbor as678 password ipexpert
neighbor as678 update-source Loopback0
neighbor 6.7.8.6 peer-group as678
neighbor 6.7.8.7 peer-group as678
neighbor 125.8.1.1 remote-as 125
!
address-family ipv4 vrf VPNB
redistribute connected
redistribute ospf 39 vrf VPNB match internal external 1 external 2
no auto-summary
no synchronization
exit-address-family
!
I don't remember very well but i think i also loaded R1 and R8 with 12.0S and
12.4 and got the same results.
And i'm using the same process id in R1 and R8. But even with different process
ids, the problem still happens.
Regards,
Antonio Soares, CCIE #18473 (R&S)
[email protected]
-----Original Message-----
From: Con Spathas [mailto:[email protected]]
Sent: domingo, 26 de Julho de 2009 9:29
To: Antonio Soares; [email protected]
Subject: Re: [OSL | CCIE_SP] VOL2 - Section 1 - Task 8.2
Gday Antonio,
I've tried to re-create the issue you described below with no luck:
10.10.18.1/32 is the R1 loopback interface for the Sham
10.10.18.8/32 is the R8 loopback interface for the Sham
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++
R1#sh ip ospf neighbor 98.9.8.8 | inc Neighbor|interface
Neighbor 98.9.8.8, interface address 10.10.18.8
In the area 0 via interface OSPF_SL0
Neighbor priority is 0, State is FULL, 6 state changes
Neighbor is up for 00:21:00
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++
R1#sh ip ospf database | beg Type-5
Type-5 AS External Link States
Link ID ADV Router Age Seq# Checksum Tag
4.0.0.4 31.3.1.1 1325 0x80000001 0x009E9A 3489661053
10.10.18.1 98.9.8.8 1282 0x80000001 0x004D4A 3489661606
10.10.18.8 31.3.1.1 1279 0x80000001 0x00E82A 3489661053
11.0.0.11 31.3.1.1 1279 0x80000001 0x00FC2E 3489661053
54.5.4.0 31.3.1.1 1325 0x80000001 0x00D130 3489661053
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++
R1#sh ip route vrf VPNB 10.10.18.8
Routing entry for 10.10.18.8/32
Known via "bgp 125", distance 200, metric 0
Tag 678, type internal
Redistributing via ospf 125
Advertised by ospf 125 subnets
Last update from 6.7.8.8 00:21:34 ago
Routing Descriptor Blocks:
* 6.7.8.8 (Default-IP-Routing-Table), from 125.125.125.2, 00:21:34 ago
Route metric is 0, traffic share count is 1
AS Hops 1
Route tag 678
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++
R8#
R8#sh ip ospf neighbor 31.3.1.1 | inc Neigh|inter
Neighbor 31.3.1.1, interface address 10.10.18.1
In the area 0 via interface OSPF_SL0
Neighbor priority is 0, State is FULL, 6 state changes
Neighbor is up for 00:22:02
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++
R8#sh ip ospf data | beg Type-5
Type-5 AS External Link States
Link ID ADV Router Age Seq# Checksum Tag
4.0.0.4 31.3.1.1 1386 0x80000001 0x009E9A 3489661053
10.10.18.1 98.9.8.8 1338 0x80000001 0x004D4A 3489661606
10.10.18.8 31.3.1.1 1341 0x80000001 0x00E82A 3489661053
11.0.0.11 31.3.1.1 1 (DNA) 0x80000001 0x00FC2E 3489661053
54.5.4.0 31.3.1.1 1386 0x80000001 0x00D130 3489661053
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++
R8#sh ip route vrf VPNB 10.10.18.1
Routing entry for 10.10.18.1/32
Known via "bgp 678", distance 200, metric 0
Tag 125, type internal
Redistributing via ospf 678
Advertised by ospf 678 subnets
Last update from 125.125.125.1 00:22:34 ago
Routing Descriptor Blocks:
* 125.125.125.1 (Default-IP-Routing-Table), from 6.7.8.7, 00:22:34 ago
Route metric is 0, traffic share count is 1
AS Hops 1
Route tag 125
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++
As you can see the Sham-Link is stable, however I have not manipulated
the Domain-Tag as shown in the OSPF database.
Tag 3489661606 = 11010000000000000000001010100110
1010100110 = AS 678
Tag 3489661053 = 11010000000000000000000001111101
1111101 = AS 125
I tried this with 12.0S and 12.4Mainline code.
Cheers,
Con.
>I found the solution to this problem !
>
>When we have a sham-link inside the same AS, there's no issues with routing
>loops with the sham-links because the external LSA will
>have the same route-tag.
>
>When we have a sham-link between two AS's, and the sham-links are advertised by
>eBGP, there's no problem because the eBGP AD is
>lower than OSPF.
>
>But when we have a sham-link between two AS's and the sham-links are advertised
>by iBGP, there's a routing loop. The routers will
>prefer the OSPF learned route instead of the iBGP because of lower AD.
>
>So the solution is to use the same "domain-tag" under the OSPF process in both
>PE's.
>
>
>
>
>Regards,
>
>Antonio Soares, CCIE #18473 (R&S)
>[email protected]
>
>-----Original Message-----
>From: [email protected]
>[mailto:[email protected]] On Behalf Of Antonio Soares
>Sent: segunda-feira, 8 de Junho de 2009 19:08
>To: [email protected]
>Subject: [OSL | CCIE_SP] VOL2 - Section 1 - Task 8.2
>
>My sham-link is flaping. As soon as the sham-link comes up, R1 and R8 start
>prefering the OSPF route instead of the iBGP route. I
>never saw this problem in regular MPLS VPNs inside one AS. In this because we
>have an Inter-AS MPLS VPN scenario ?
>
>+++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>R1#
>00:03:31: %OSPF-5-ADJCHG: Process 39, Nbr 8.8.8.8 on OSPF_SL0 from LOADING to
>FULL, Loading Done
>R1#
>R1#sh ip route vrf VPNB | inc 8.8.8.8
>B 8.8.8.8 [200/0] via 6.7.8.8, 00:00:14
>R1#
>R1#
>00:03:47: %OSPF-5-ADJCHG: Process 39, Nbr 8.8.8.8 on OSPF_SL0 from FULL to
>DOWN, Neighbor Down: Interface down or detached
>R1#
>R1#sh ip route vrf VPNB | inc 8.8.8.8
>O E2 8.8.8.8 [110/1] via 6.7.8.8, 00:00:00
>R1#
>+++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>R8#
>00:06:28: %OSPF-5-ADJCHG: Process 39, Nbr 1.1.1.1 on OSPF_SL0 from LOADING to
>FULL, Loading Done
>R8#
>R8#sh ip route vrf VPNB | inc 1.1.1.1
>B 1.1.1.1 [200/0] via 125.125.125.1, 00:00:13
>R8#
>R8#
>00:06:44: %OSPF-5-ADJCHG: Process 39, Nbr 1.1.1.1 on OSPF_SL0 from FULL to
>DOWN, Neighbor Down: Interface down or detached
>R8#
>R8#sh ip route vrf VPNB | inc 1.1.1.1
>O E2 1.1.1.1 [110/1] via 125.125.125.1, 00:00:02
>R8#
>+++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>
>After a few hours trying to understand why this was happening, i was able to
>make it work tweaking the OSPF AD for the External
>routes in R1 and R8.
>
>Anyone saw this problem in this lab ?
>
>And why in the PG we don't see the sham-link interfaces in R3 and R9 ?
>
>
>Regards,
>
>Antonio Soares, CCIE #18473 (R&S)
>[email protected]
>
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