MPLS Grey Areas

[zikalamc]

Hi All,

-Are routing protocol contexts seperate copies of VPN routing instances or seperate copies of routing protocol onstances? Please explain.

-Does Cisco sometimes use the word "P-router" to refer to a PE router, if so under what circumstances?

-tag atm maxhops, is command used beacuse the LFIB can get too large in cell-mode or is it used due to the shortcomings of TDP?

-In cell-mode, do we use a vpi/vci to send data to a CE or do we use a routing table.

-In mpls aware ATM networks, must PVCs be created manually? If so why cause there's TDP/LDP?

-Is it mandatory/recommended to always include the outgoing interface when configuring a vrf static route.

[Harold Ritter]

- For all routing protocol but OSPF, the same process is used. CSCdz47082 changes the OSPF behavior to be the same as the other routing protocols. So you have multiple instances under the same under the same protocol data block (PDB).

- P and PE are in function to the functionality they provide. P is only involved in label switching (swap), whereas the PE does label imposition and disposition (pop and push). If for a given LSP the PE acts purely as a transit (doesn't terminate or originate the LSP), you could say that this PE is a P for that LSP.

- "tag atm maxhops": According to documentation, this mechanism is used to prevent forwarding loops in the setting up of label switch paths across an ATM region.

- The VPN label is learnt via BGP whether you use cell or frame mode. The label put in the vpi/vci is only used to get traffic from ingress to egress PE. The label learnt via BGP is used to direct the traffic to the correct VRF once the traffic reaches the egress PE.

- in mpls aware atm the PVC is replaced by the LSP, hence LDP/TDP.

- Not mandatory. The next hop has to be resolvable using the VRF though unless the "global" keyword is used.

Hope this helps,

[Harold Ritter]

Let me re-phrase my first statement. For all routing protocol but OSPF, the same protocol data block (PDB) is used for all instances (processes). So it is multiple processes under the same PDB, which makes the IOS 32 PDB limitation irrelevant anymore since each PDB now has multiple processes.

Hope this helps,