MPLS VPN VRF Export Map

Lessons Discussion
#1

This topic is to discuss the following lesson:

#2

Thanks Rene - so am I right in thinking there is no implicit deny on a route map used as an export map in this process? Anything not matched on the route-map will just use the default settings configured.

Normally when applying a route-map to a neighbour in IPv4 (e.g. neighbor X route-map Y) if something isn’t positively matched in the route-map, it will get dropped?

#3

Hi Chris,

It still has the implicit deny but when you use a route-map as an export-map, it only tells the router which route-targets to add. When you use a route-map with a neighbor for a routing protocol, it works as a filter for routes.

For example, this is the default route-target on PE1:

ip vrf CUSTOMER
 rd 1:1
 route-target export 1:1:

And we use this export-map:

PE1(config)#ip prefix-list CE1_L0 permit 1.1.1.1/32
PE1(config)#route-map EXPORT_MAP permit 10
PE1(config-route-map)#match ip address prefix-list CE1_L0

Then we end up with:

PE1#show ip bgp vpnv4 all 1.1.1.1/32 | include Extended
      Extended Community: RT:3:3 OSPF DOMAIN ID:0x0005:0x000000020200
PE1#show ip bgp vpnv4 all 11.11.11.11/32 | include Extended
      Extended Community: RT:1:1 OSPF DOMAIN ID:0x0005:0x000000020200
PE1#show ip bgp vpnv4 all 192.168.12.0/24 | include Extended
      Extended Community: RT:1:1 OSPF DOMAIN ID:0x0005:0x000000020200

Because of the implicit deny, the last two routes didn’t get route-target 3:3 but the default one (1:1).

Hope this helps!

Rene

#4

Hi Rene,

Thank you for your nice lesson . Need to know more about the “Additive” keyword functionality . Can you please more brief on it?

BR//ZAMAN

#5

Hello Zaman

The additive keyword will allow you to add an export map without overwriting the previously configured ones. For example, if you configure the following:

PE1(config)#route-map EXPORT_MAP permit 10         
PE1(config-route-map)#set extcommunity rt 1:1

and then at a later time you configure this:

PE1(config)#route-map EXPORT_MAP permit 10         
PE1(config-route-map)#set extcommunity rt 3:3

The result is that the 1:1 entry will be overwritten by the 3:3 entry. However, if you use the additive keyword like this instead:

PE1(config)#route-map EXPORT_MAP permit 10         
PE1(config-route-map)#set extcommunity rt 3:3 additive

Then 3:3 will not overwrite 1:1 but will be added to it.

I hope this has been helpful!

Laz

#6

Hi @lagapides
So will this additive keyword still cause my routes to stay at the other end PE orwill it be removed from the far end PE node ?

#7

Hello Kushagra

The export maps, as well as the additive keyword, will only make changes to the routes within the same PE device. They will not affect the PE node at the other end. Any changes required at the node at the other end must be made locally.

I hope this has been helpful!

Laz

#8

Hi Rene,

Don’t we need to remove route-target export <r:t> command when we enter export-map <RM> command when filtering vpnv4 routes?

#9

Hello Roshan

It’s not necessary to remove the route-target command from the VRF configuration because the export map will actually overwrite the RT that is set with the route-target command. Actually, it’s a good idea to keep the route-target command in place, because you may not want to replace it completely, but you may want to change the RT only for specific routes using a prefix list. For example, in the lesson, the route target was set to 1:1 for all routes, but you selectively stated that you wanted the RT of 1.1.1.1/32 to become 3:3. By implementing this, the rest of the routes remained with an RT of 1:1 (which is achieved by the initial route-target command) and only the desired destination was changed.

I hope this has been helpful!

Laz

#10

Hello,
it is possible to filter local labels for VRFs? I can just find label filtering in the global routing table.

Restrictions for MPLS LDP Local Label Allocation Filtering
• Label Distribution Protocol (LDP) local label allocation configuration for prefix list or host routes is supported only in the global routing table.

https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/mp_ldp/configuration/xe-16/mp-ldp-xe-16-book/mp-ldp-alloc-filter.html

Thanks a lot.

Regards,

Lukas

#11

Hello Lukas

The MPLS LDP Local Label Allocation Filtering feature is limited to functioning on the global routing table and cannot achieve what you are looking for. However, using route-maps, you can filter which routes should get exported and what route-targets should be used. You can find out more about how to do this at the following lesson:

I hope this has been helpful!

Laz

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#12

Thanks a lot for your reply :slight_smile:

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