Flash Cards - BGP / MPLS

Three kinds of LSRs exist in an MPLS network:

Ingress LSRs — Ingress LSRs receive a packet that is not labeled yet, insert a label (stack) in front of the packet, and send it on a data link.

Egress LSRs — Egress LSRs receive labeled packets, remove the label(s), and send them on a data link. Ingress and egress LSRs are edge LSRs.

Intermediate LSRs — Intermediate LSRs receive an incoming labeled packet, perform an operation on it, switch the packet, and send the packet on the correct data link.

An LSR can do the three operations: pop, push, or swap.

An LSR that pushes labels onto a packet that was not labeled yet is called an imposing LSR.

An LSR that removes all labels from the labeled packet before switching out the packet is a disposing LSR.

A label switched path (LSP) is a sequence of LSRs that switch a labeled packet through an MPLS network or part of an MPLS network.

The ingress LSR of an LSP is not necessarily the first router to label the packet. The packet might have already been labeled by a preceding LSR. Such a case would be a nested LSP—that is, an LSP inside another LSP.

A Forwarding Equivalence Class (FEC) is a group or flow of packets that are forwarded along the same path and are treated the same with regard to the forwarding treatment. However, not all packets that have the same label belong to the same FEC, because their EXP values might differ; the forwarding treatment could be different, and they could belong to a different FEC.

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BGP

To choose an exit point when you have multiple.

access-list 1 per 10.1.1.0 0.0.0.255

Route-Map Oscar
match ip address 1
set ext-community cost 1 1

#neighbor x.x.x.x route-map in

#router bgp 100
distance 150 x.x.x.x (source) x.x.x.x (subnet of source) <1 _ ACL is route to change the distance on>

#router bgp 100
distance bgp <external> <internal> <local>

#router bgp 100
no bgp fast-external failover
advertisement-interval <iBGP> <eBGP>

Route-Reflector Attributes (Optional Non-Transitive)

i. Origin ID - Router ID of the router that originated the prefix.
ii. Cluster ID - RR ID & Clients
iii. Cluster List - Same as the AS_Path (Loop Avoidance), if RR see's it's own ID it will drop the packet.

BGP Neighbor ORF

This has to be done on both sides or this will not work.

#ip prefix-list <name> permit x.x.x.x/x le 32
#neighbor x.x.x.x prefix-list <name> in
#address-family ipv4 unicast
#neighbor x.x.x.x capability orf prefix-list <send | receive | both>
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#ip as-path access-list 1 deny ^300$
#ip as-path access-list 1 permit .*

#neighbor x.x.x.x filter-list 1 in

Using an extended ACL to advertise networks - With BGP it is different.

access-list 101 permit (network) (mask) (mask) (mask)