MPLS TE issue

[limtohsoon]

Hi Sir,

I'm doing a lab test on MPLS TE. Please see attached slides.

In Scenario 1, there's only a single link between R1 and R2. The TE tunnel from R3 to R1, traversing thru R2, is up & operational.

In Scenario 2, a new link is added between R1 and R2, with the same bandwidth value as the first link. Thus, producing equal-cost multipath between R1 and R2. On R3, I modify the ip explicit-path next-address to point to R1's TE router-id instead. And the TE tunnel goes down. Theoretically, I understand that we can point to either next-hop address or next-hop TE router-id.

Please advise what's the correct config for Scenario 2.

Thank you.

B.Rgds,

Lim TS

[limtohsoon]

Hi Harold,

The complete config is as follows:

--------------------------------------------------------------

!

hostname R3

!

interface FastEthernet0/0

ip address 172.18.253.6 255.255.255.252

mpls label protocol ldp

mpls traffic-eng tunnels

mpls traffic-eng backup-path Tunnel20

mpls ip

!

interface Tunnel2

description *** Primary TE Tunnel to R1 ***

ip unnumbered Loopback0

mpls ip

tunnel destination 172.18.255.2

tunnel mode mpls traffic-eng

tunnel mpls traffic-eng autoroute announce

tunnel mpls traffic-eng priority 1 1

tunnel mpls traffic-eng path-option 1 explicit name path_to_R1

tunnel mpls traffic-eng record-route

tunnel mpls traffic-eng fast-reroute

!

interface Tunnel20

description *** Backup TE Tunnel to R1 ***

ip unnumbered Loopback0

mpls ip

tunnel destination 172.18.255.2

tunnel mode mpls traffic-eng

tunnel mpls traffic-eng priority 1 1

tunnel mpls traffic-eng path-option 1 explicit name path_to_R1_backup

tunnel mpls traffic-eng record-route

!

ip explicit-path name path_to_R1 enable

next-address 172.18.255.1

next-address 172.18.255.2

!

ip explicit-path name path_to_R1_backup enable

exclude-address 172.18.253.5

!

--------------------------------------------------------------

If Fa0/0 is down on R3, when I do "sh ip route 172.18.255.2", should I see it points to Tu2 or Tu20? Now that I have the "mpls traffic-eng backup-path Tunnel20" command on Fa0/0.

In an actual deployment with similar config, when the protected link is down, it still point to primary tunnel to reach the tailend, but via an alternative path. In that case, it's not triggering FRR?

Please help.

Thank you.

B.Rgds,

Lim TS

[Harold Ritter]

Lim,

"show ip route 172.18.255.2" still displays Tu2 as the outgoing interface when Fa0/0 is down.

"show ip cef 172.18.255.2" gives you more information and tells you that Tu20 is actually being used for fast tag rewrite if FRR has been triggered.

"sh mpls traff fast data" is another helpful command while trying to determine whether FRR is being triggered. The "active" status indicates that FRR kicked in properly after the physical link (Fa0/0) failure. Under normal condition, the status should be set to "ready".

Hope this helps,

[Harold Ritter]

Lim,

Just as a precision.

Bear in mind that the protection tunnel (Tu20) does not replace the protected tunnel (Tu2) but rather works in conjunction with it.

This is why it is normal to see the protected tunnel has the outgoing interface even when fa0/0 is down.

Hope this helps,

[Harold Ritter]

Lim,

Here's a couple of comments about the config:

1- If you want tun2 to use FRR, you need to configure it specifically as follow:

interface Tunnel2

tunn mpls traffic-eng fast-reroute

2- For the FRR backup tunnel, the only thing you need to make sure is that you don't set it up using the physical link you are protecting as follow.

ip explicit-path name path_to_R1_backup enable

exclude-address 172.18.253.5

3- You don't need the loose option for the explicit path on the primary tunnel. You could configure as follow:

ip explicit-path name path_to_R1 enable

next-address 172.18.253.5

next-address 172.18.255.2

Hope this helps,

[Harold Ritter]

My mistake.

3- I missed the fact that you were going from interface specific to looback address. You could have gone all the way specifying loobback addresses as follow:

ip explicit-path name path_to_R1 enable

next-address 172.18.255.1

next-address 172.18.255.2

but if you are going from interface address to loopback then you indeed need the loose option as follow:

ip explicit-path name path_to_R1 enable

next-address 172.18.253.5

next-address loose 172.18.255.2

Hope this helps,

[r.hew]

Hi Harold,

Let me introduce myself first, I'm Lim's mentor.

Thanks for the clarification. This seems to be a very good advice.

P/S: Also thanks to Network.King for the guidelines.

Best Regards,

Raymond Hew

[Harold Ritter]

Hello,

Nice to meet you. Always a pleasure to help.

Regards,