What are aggregate labels !

[Jonn cos]

Hi all experts.

Can someone explain me what is the meaning of aggregate when i do show mpls forwarding table. I tried searching here but it seems its meaning changes in different contexts. Like in mpls vpn, it means that this packet is for a VRF and needs a RIB lookup or something like that can someone help me understand it pls

[Ivan Krimmel]

John,

as the name implies, 'aggregate' means that a few FECs received one common label, which will be used while forwarding to any of them. That usually happens as a result of summarization.

Cheers!

[rsimoni]

Hi John,

yes indeed aggregate label means that a layer3 lookup is needed to forward the packet.

Aggregate labels are assigned by routers (PE's) in mpls vpn context to all the local IP addresses for a given vrf to save label space.

They are assigned to locally conected netwoeks and are also assigned to aggregate prefixes to (i.e. BGP summarization)

I.e. if your PE for vrf red has 4 interfaces, 1 loopback interface and 3 interfaces facing CE's routers, they will all share the same aggregate label.

When traffic destined to that label (so either destined to the router or to the PE-CE subnet) reaches the PE it needs to perform an extra lookup in the RIB to see to find the next hop and the outpgoing interface.

Riccardo