SHAM-LINK NOT WORKING

[isaaco001]

Dear Community,

I kindly asking for assistance on a sham-link issue. I have configured R2 and R4 as the PE routers,R3 as the P router ,R1 and R5 as CE routers.

I enable sham-link configs in the loopback interfaces,vrf interface and ospf process 20 vrf A.I have tried to manipulate the cost so that the backdoor link is not used by setting the metric to maximum but still the next-hop goes to the backdoor link.Why wont the sham-link take effect and set the next hop as the PE router which are R2 or R4 but not to CE routers?Attached are all the run config files and topology.

Thank you all.

Regards,

Isaac.

[Rolf Fischer · Accepted solution]

Isaac,

the sham-link is in area 20 whereas the backdoor- and local links are in area 0, so the intra-area path through area 0 is prefered regardless of the higher costs.

When you put the sham-link in area 0 it should work as desired.

HTH
Rolf

[isaaco001]

Hi Rolf,

You are right about the area 20 affecting path preference,thanks for the help.I have ,however ,ran into an issue where by the prefixes at the CE routers are still using the backdoor link despite the fact the sham link has a lower cost of 1 and back door 10. I have attached the configs with relevant show cmds.In the attached configs, 5.5.5.5 loopback belongs to R5 but is learnt through backdoor despite the other route 192.168.45.0 being learnt through sham-link.

Thanks.

Regards,

Isaac.

[isaaco001]

Rolf,

I changed the metric of the backdoor to max(65535) and it worked!Now all routes prefer sham-link.Thanks.

Regards,

Isaac.

[Rolf Fischer]

Isaac,

sorry - I couldn't see your reply till now, apparently they had some problems with the forum again...

Anyway, thanks for your feedback and thanks for using the rating system!

Regards,

Rolf