The MPLS-OPS Archive

[Robert Raszuk <raszuk@cisco.com>]

Hi Lian,

> My understanding is that the load-balancing is provided solely
> based on the LSP(s) built in between the ingress PE and egress PE,
> and it has nothing to do what is encapsoluated inside the label
> packet because the P router has no idea of the VPN routes.

Not quite. For the IP packets we usually do look at the IP header to get
the IP src/dst. It is true that P routers don't have a clue about VPN
addresses, but that does not matter - no lookup is not done based on
them - just the hash mapping. Now what do we map this has to - basically
tag_loadinfo which in turn is build from cef loadinfo's. That in turn is
build from IGP. 

So why do we bother to do this - simply to get better traffic
distribution then just based on the hash created from label stack
itself. 

Said all this I regred to say that some platforms and in particular some
line cards (mostly on GSR or OSR) can't look high enough and all they do
is the hash based on the labels only present on the stack.

Rgs,
R.

> LIAN Franklin FTLD/IAP wrote:
> 
> Hello,
> 
> Is there anybody from Cisco can explain how the implementation of
> load-balancing is done on the P router in MPLS core?  Let's say
> we have MPLS L3 VPN and MPLS L2 VPN in place, my question is how
> the P router provides load-balancing between two customer sites
> if two or more equal paths between the two sites exist on a given
> P router?
> 
> My understanding is that the load-balancing is provided solely
> based on the LSP(s) built in between the ingress PE and egress PE,
> and it has nothing to do what is encapsoluated inside the label
> packet because the P router has no idea of the VPN routes.
> I will appreciate if somebody on the list can correct me if I am
> wrong.
> 
> Thanks in advance,
> Franklin
> 
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