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RD & RT

Aneek
Beginner
Beginner

If RT makes the unique decision of filtering the routes into the right VRF Instance, then why RD might be required?

 

4 Replies 4

Giuseppe Larosa
Hall of Fame Master Hall of Fame Master
Hall of Fame Master

Hello @Aneek ,

The RD provides the capability to support address overlapping in different VRFs on the same node.

If both VRF A and VRF B have the prefix 10.10.10.0/24 how to discriminate between them ?.

 

In addition to this, the RD is a component of the VPNv4 NLRI

VPNv4 NLRI =   RD:<IPv4+prefix>  + VPN MPLS label

 

The route target provides a color to the VPNv4 route and allows remote PE nodes in importing to decide if the VPNv4 prefix is of interest for one or more locally defined VRFs or for none.

The route target is a BGP attribute of type extended community, the RD is part of the VPNv4 NLRI definition.

 

The use of differentiated per PE RD values for the same VPN allows route reflector to propagate multiple paths to client PE nodes that if using the same RD would lead to a single best path propagation (the best path would be likely the source PE with the lowest BGP RID if the IGP cost is the same)

Note: the above applies to a VRF site multihomed to two PE nodes for greater redundancy.

 

Multiple route targets can be associated to a VPNv4 NLRI but only a single RD is part of it.

 

Hope to help

Giuseppe

 

balaji.bandi
VIP Guru VIP Guru
VIP Guru

RD is required only if you more customer having the same address space overlap.

 

Like Customer A having 192.168.1.0/24

Like Customer  B having 192.168.1.0/24

 

 

 

BB

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Hello @balaji.bandi ,

the RD is always required when configuring a VRF it is part of its mandatory configuration ( it may be automatically created this is true).

Route targets can be omitted in contexts like VRF lite if there is no need to import / export routes between different VRFs.

 

Hope to help

Giuseppe

 

Sure @Giuseppe Larosa  Agreed and  thanks for the input and clarity. i have only given use case where more benifical with RD.

BB

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