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Configuring MPLS VPN using static routing

Hi,

I am managed to set up a BGP/MPLS VPN in a laboratory using CS3620 routers running IOS 12.2(3) with ISIS. I am thinking of using static routes among the PE and P routers instead of a IGP. Does anyone know if Cisco routers supports static configuration of LSP? I have tried but could not get it work.

1 ACCEPTED SOLUTION

Accepted Solutions

Re: Configuring MPLS VPN using static routing

You can very well run MPLS with static routing in the core, as in Cisco we have to meet 2 criterias to have a MPLS forwarding Table.

1) Creating the LIB

This thing lies in having LDP neighborship netween two peers and you have Label bindings.

This is irrespective of what is the best next hop to reach the advertising peers LDP_ID.

2) Creating the LFIB

Now after considering all the Label bindings, the LDP_ID which can be reached out an interface

as a next hop, those Label bindings get installed in the LFIB.

So considering the above two points, we have to be careful in static routes

only for interfaces like Ethernet (Multiaccess Segments).

As in CEF when you give a static route pointing to an Ethernet Interface, CEF creates a

GLean Adjacency (Meaning there could be multiple hosts as the next hop on this segement, and it will glean for the right next-hop)

Now you may observe that when you give a static route only pointing to an Ethernet interface,

you LDP adjacency may come up and you may exchange the bindings with each other. But the Label Forarding Table is not created. This is bcos of this being a Multiaccess interface. And you have

Glean For it. If its a Normal WAN interface like Serial or POS, then there is no problem of

GLean and you would have a Valid Cached Adjacency.

So to avoid probelems with Ethernet interfaces you can simply specify the next-hop-ip address.

For Eg: ip route 10.10.31.250 255.255.255.255 10.10.31.226 (Without the Interface)

ip route 10.10.31.250 255.255.255.255 fa0/0 10.10.31.226 (Or with the Interface)

Only Difference in both is in the first one it has to do a recursive lookup for the outgoing interface. Otherwise both work well. And you can have static routes in your network

running MPLS.

And doing this CEF would would work as it should and you would have a Valid Cached Adjacency.

So this is applicable for Cisco devices which use CEF, including 6500 with SUP720.

HTH-Cheers,

Swaroop

7 REPLIES

Re: Configuring MPLS VPN using static routing

Hello,

static routing the the core is supported. Just make sure you have connectivity between all loopback addresses (for BGP and LDP). This might involve quite a number of static routes and a single one missing might break everything.

Can you post your configs (MPLS relevant part)? Maybe we can pinpoint the problem.

Regards, Martin

New Member

Re: Configuring MPLS VPN using static routing

Hi Martin,

Thanks for the reply. I have 4 LSR namely PE1, P1, P2 & PE2 that forms the MPLS core.

Attached is the config for PE1, P2 & PE2

I have no connectivity problem between the LSRs. However, my MPLS forwarding table for each LSR has no tags. Do I have to manually create them, i.e. to bind the tags to the prefixes or do I expect the label distribution is done automatic?

regards, Rod

Re: Configuring MPLS VPN using static routing

Hi,

Give the Interface and Next-hop in all the static routes .

Just taking a single route as eg in p2:

ip route 10.1.1.10 255.255.255.255 FastEthernet1/0 10.1.1.10

Hope this helps:

regards

vanesh k

New Member

Re: Configuring MPLS VPN using static routing

I have similar scenario except that I want to use two PEs and eliminate the two P routers, is it possible??

Secondly, I intend to achieve the solution using Cisco 6506 (with supervisor engine 720 and policy feature card) as my PEs, will that be achievable? if yes what other add-on cards will be necessary??

Re: Configuring MPLS VPN using static routing

You can very well run MPLS with static routing in the core, as in Cisco we have to meet 2 criterias to have a MPLS forwarding Table.

1) Creating the LIB

This thing lies in having LDP neighborship netween two peers and you have Label bindings.

This is irrespective of what is the best next hop to reach the advertising peers LDP_ID.

2) Creating the LFIB

Now after considering all the Label bindings, the LDP_ID which can be reached out an interface

as a next hop, those Label bindings get installed in the LFIB.

So considering the above two points, we have to be careful in static routes

only for interfaces like Ethernet (Multiaccess Segments).

As in CEF when you give a static route pointing to an Ethernet Interface, CEF creates a

GLean Adjacency (Meaning there could be multiple hosts as the next hop on this segement, and it will glean for the right next-hop)

Now you may observe that when you give a static route only pointing to an Ethernet interface,

you LDP adjacency may come up and you may exchange the bindings with each other. But the Label Forarding Table is not created. This is bcos of this being a Multiaccess interface. And you have

Glean For it. If its a Normal WAN interface like Serial or POS, then there is no problem of

GLean and you would have a Valid Cached Adjacency.

So to avoid probelems with Ethernet interfaces you can simply specify the next-hop-ip address.

For Eg: ip route 10.10.31.250 255.255.255.255 10.10.31.226 (Without the Interface)

ip route 10.10.31.250 255.255.255.255 fa0/0 10.10.31.226 (Or with the Interface)

Only Difference in both is in the first one it has to do a recursive lookup for the outgoing interface. Otherwise both work well. And you can have static routes in your network

running MPLS.

And doing this CEF would would work as it should and you would have a Valid Cached Adjacency.

So this is applicable for Cisco devices which use CEF, including 6500 with SUP720.

HTH-Cheers,

Swaroop

New Member

Re: Configuring MPLS VPN using static routing

Thanks for the enlightenment and the recommendation, Swaroop. My problem is solved.

regards

Rod

New Member

Re: Configuring MPLS VPN using static routing

Thanks Vanesh, your recommendation helps. My problem is solved.

regards

Rod

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