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Community Member

Controlling rd,,, MPLS VPN

Is it possible to control route distinguisher?

The RD does not by itself impose any semantics; it contains no

information about the origin of the route or about the set of VPNs to

which the route is to be distributed. The purpose of the RD is

solely to allow one to create distinct routes to a common IPv4

address prefix. -> Other means are used to determine where to

redistribute the route

6 REPLIES
Community Member

Re: Controlling rd,,, MPLS VPN

Hi,

You can give RD only on the VRF configuration part staticly. I didn' see any other method , command to control RD on Cisco. I also couldn't see any reason to do it!

Regards

Community Member

Re: Controlling rd,,, MPLS VPN

Thank you for your answer.

If we can control rd, it will be useful.

RFC 2547 said:

One may have one route to a given system for packets from the extranet (where the route leads to a firewall), and a different route to the same system for packets from the intranet (including packets that have already passed through the firewall).

Community Member

Re: Controlling rd,,, MPLS VPN

Hi,

I also read the RFC. This is written :

"

The per-site forwarding tables in a PE are ONLY used for packets

which arrive from a site which is directly attached to the PE. They

are not used for routing packets which arrive from other routers that

belong to the SP backbone. As a result, there may be multiple

different routes to the same system, where the route followed by a

given packet is determined by the site from which the packet enters

the backbone. E.g., one may have one route to a given system for

packets from the extranet (where the route leads to a firewall), and

a different route to the same system for packets from the intranet

(including packets that have already passed through the firewall).

"

I couldn't correlate any relation with RD. On the router different VRF s uses different routing tables. There is no RD affect if there is only 1 router but different VRFs. RD is only used by MP-BGP to diffrenciate the same route belonging to different VPNs. RD usage is especially very important on P routers BGP route selection process which has no VRF inside itself.

Regards

Community Member

Re: Controlling rd,,, MPLS VPN

hi, mazahr.

Suppose that you have 2 Gateways to internet.

2 Gateways advertise several routes for the network prefix simultaneously.

If you control rd as well as rt, you will have different routes per vrf.

E.g. suppose that one site import routes from 2 Gateway. For specific prefix,

you can choose one gateway according to rd, if you can control rd.

% bgp received routes

1:1.1.1.1 next hop Gateway 1 <- I will choose this route because rd is 1.

2:1.1.1.1 next hop Gateway 2

regards.

Community Member

Re: Controlling rd,,, MPLS VPN

Hello,

As I said there is no command or method at least today using RD except static config. But as you also know your goal can be achieved using many methods inside MP-BGP

Regards

Community Member

Re: Controlling rd,,, MPLS VPN

No. There is no way to control the RD. The primary purpose of RD is to create unique IPv4 address within the VRF. To control route distribution use the Import and Export Route targets.

check out http://www.cisco.com/univercd/cc/td/doc/product/rtrmgmt/vpnsc/mpls/1_1/user_gd/vpn_ug1.htm#15737

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