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

[network.king]

Hi ,

When configuring the explicit path with next-hop as Router-id , use the loose option

next-address loose 172.18.255.2

If ur ios doesnt support , no other go , u need to go with the interface ip only.

Hope this helps

regards

vanesh k

[limtohsoon]

Hi Vanesh,

Should I modify my config as follows:

!

ip explicit-path name path_to_R1 enable

next-address 172.18.253.5

next-address loose 172.18.255.2

!

Thank you.

B.Rgds,

Lim TS

[network.king]

Hi Lim,

Yes , pls do the same and let us know the result

regards

vanesh k

[limtohsoon]

Hi Vanesh,

My problem description is not complete. In actual scenario, R3 has an alternative path to R1. And I'm implementing FRR link protection for the interface Fas0/0 on R3.

Back to my Scenario 2, if I were to implement FRR, would the following config work?

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

!

hostname R3

!

interface Tunnel2

description *** TE Tunnel to R1 ***

ip unnumbered Loopback0

tag-switching 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

!

interface Tunnel20

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

ip unnumbered Loopback0

tag-switching 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

!

interface FastEthernet0/0

mpls traffic-eng backup-path Tunnel20

!

ip explicit-path name path_to_R1 enable

next-address 172.18.253.5

next-address loose 172.18.255.2

!

ip explicit-path name path_to_R1_backup enable

exclude-address 172.18.253.5

exclude-address 172.18.255.2

!

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

I'm not very sure about the configuration of the "exclude-address".

Please advise.

Thank you.

B.Rgds,

Lim TS

[network.king]

Hi Lim,

Iam not sure abt your complete topolgy , but if you want the TE tunnel to be made up on Loopback address , you need to give the loose option .

ip explicit-path name path_to_R1_backup enable

next-address loose 172.18.255.2

and ur igp running on the second link from R3 to R1 would take care .

Hope this helps

regards

vanesh k

[Harold Ritter]

Vanesh,

Just as a precision, the loose option only needs to be used if the next-address does not belong to a directly connected router. You could use all loopback addresses in your explicit path without using the loose option.

Hope this helps,

[limtohsoon]

Hi Varesh,

For e.g. in Scenario 1, my usual practice of configuring TE with FRR is as follows:

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

!

hostname R3

!

interface Tunnel2

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

tunnel destination 172.18.255.2

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

tunnel mpls traffic-eng fast-reroute

.

!

interface Tunnel20

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

tunnel destination 172.18.255.2

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

.

!

ip explicit-path name path_to_R1 enable

next-address 172.18.253.5

next-address 172.18.253.14

!

ip explicit-path name path_to_R1_backup enable

exclude-address 172.18.253.5

exclude-address 172.18.253.14

!

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

In the case of Scenario 2, if I have the following explicit-path config for the primary tunnel:

!

ip explicit-path name path_to_R1 enable

next-address 172.18.253.5

next-address loose 172.18.255.2

!

or what Harold suggested:

!

ip explicit-path name path_to_R1 enable

next-address 172.18.255.1

next-address 172.18.255.2

!

Then, how should I configure the explicit-path for the backup tunnel using the exclude-address command?

Please help.

Thank you.

B.Rgds,

Lim TS

[limtohsoon]

Hi Varesh, Harold -

Attached is the complete network diagram. Please look at Scenario 3.

I'm building a primary TE tunnel from R3 to R1 via R2. The backup tunnel will go via R4.

I'm unsure about the configuration of the explicit-path for both primary & backup tunnels. From the info you all provided, the explicit-path for primary tunnel will be either one of the following config:

!

ip explicit-path name path_to_R1 enable ---> Suggested by Varesh

next-address 172.18.253.5

next-address loose 172.18.255.2

!

or

!

ip explicit-path name path_to_R1 enable ---> Suggested by Harold

next-address 172.18.255.1

next-address 172.18.255.2

!

I'm concerned about how to configure the explicit-path for backup tunnel, if I were to use exclude-address.

Please advise.

Thank you.

B.Rgds,

Lim TS

[Harold Ritter]

Lim,

My two other comments are still valid:

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

Hope this helps,

[limtohsoon]

Hi Harold,

I do have the command "tunnel mpls traffic-eng fast-reroute" under interface Tunnel2 on the actual router. Somehow I forgot to include it in my post. Please excuse me.

So, I'll be configuring the following explicit-path on R3:

!

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

!

Is that right?

Thank you.

B.Rgds,

Lim TS

[Harold Ritter · Accepted solution]

That seems to be right. Try it and let me know if it works for you.

Hope this helps,

[limtohsoon]

Hi Harold,

I'm trying the config on some C3640 routers in a lab. Your suggestion for explicit-path configuration for the primary tunnel works; tunnel2 comes up. I can't test FRR because it's not supported on the C3640.

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

R3#sh mpls tra tu tu 2

Name: *** Primary TE Tunnel to R1... (Tunnel2) Destination: 172.18.255.2

Status:

Admin: up Oper: up Path: valid Signalling: connected

path option 1, type explicit path_to_R1 (Basis for Setup, path weight 65635)

path option 2, type dynamic

Config Parameters:

Bandwidth: 0 kbps (Global) Priority: 1 1 Affinity: 0x0/0xFFFF

Metric Type: TE (default)

AutoRoute: enabled LockDown: disabled Loadshare: 0 bw-based

auto-bw: disabled

InLabel : -

OutLabel : FastEthernet0/0, 19

RSVP Signalling Info:

Src 172.18.255.5, Dst 172.18.255.2, Tun_Id 2, Tun_Instance 5050

RSVP Path Info:

My Address: 172.18.255.5

Explicit Route: 172.18.253.5 172.18.253.54 172.18.255.2

Record Route:

Tspec: ave rate=0 kbits, burst=1000 bytes, peak rate=0 kbits

RSVP Resv Info:

Record Route: 172.18.253.5 172.18.253.54

Fspec: ave rate=0 kbits, burst=1000 bytes, peak rate=0 kbits

Shortest Unconstrained Path Info:

Path Weight: 65635 (TE)

Explicit Route: 172.18.253.5 172.18.253.54 172.18.255.2

History:

Tunnel:

Time since created: 1 days, 17 hours, 25 minutes

Time since path change: 19 minutes, 41 seconds

Current LSP:

Uptime: 19 minutes, 41 seconds

Selection: reoptimation

Prior LSP:

ID: path option 1 [5049]

Removal Trigger: path error

R3#

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

I'm implementing this on my customer network with C7609 routers. Will have to test FRR on the live network then. Will keep you posted.

Thank you.

B.Rgds,

Lim TS

[limtohsoon]

Hi Harold,

Referring back to my lab test Scenario 3, a primary TE tunnel (int Tunnel2) is built from R3 to R1 via R2. FRR is used to protect the Fas0/0 link on R3, using backup Tunnel20.

Theoretically, when I execute the following commands on R3:

(1) sh ip route 172.18.255.2 - I should see it points to Tunnel2.

(2) sh mpls tra tu tu 2 - I should see Tunnel2 takes the path R3->R2->R1.

(3) sh mpls tra tu tu 20 - I should see Tunnel20 is pre-signalled and taking the path R3->R4->R1.

Is it right?

Interface Tunnel2 has only one path-option pointing to the explicit-path R2->R1.

If Fas0/0 is down on R3, when I do "sh ip route 172.18.255.2", should I see it points to Tu2 or Tu20?

In actual deployment and testing (with slightly different scenario than the lab), I notice the router still points to its primary tunnel (taking an alternative path this time to reach the tunnel tailend), when the protected link is down.

I'll elaborate on my actual scenario in another post. Hope you can help.

Thank you.

B.Rgds,

Lim TS

[Harold Ritter]

(1) Correct.

(2) Correct.

(3) Correct.

When Fa0/0 goes down, 172.18.255.2 should still point at Tu2. Tu20 simply provides Node/Link Protection.

Hope this helps,