[c-nsp] Best practice - Core vs Access Router

Andy B. globichen at gmail.com
Tue Feb 9 02:58:59 EST 2010

I am running one 6509 as a core router:

1x WS-SUP720-3BXL
1x WS-X6748-GE-TX
2x WS-X6704-10GE

On this core I am doing BGP with 2 upstreams (full BGP table IN) and
10 downstreams (full BGP table OUT).
I am also doing OSPF with 4 other core routers in this AS.

On top of that there is one VLAN on this core that serves as a default
gateway for approximatively 5000 servers, producing around 30 GBps
outbound traffic and 10 GBps inbound.

Recently I noticed that this core router becomes very unresponsive
from time to time, dropping OSPF and BGP sessions (hold time expired
and so on). SNMP generated stats become useless as well, because most
SNMP requests to that core are timing out. It's really just the core
that is rather slow, but reachability to my customers and from my
customers to the internet remains perfect. Pinging the loopback
interface of the core or any default gateway IP address of the busy
VLAN can show up to 60% packet loss

Therefore I was thinking to split the core and move this very active
VLAN to a different router behind the core and only add a static route
to the core, so that the new router can handle these many MAC
addresses and hopefully get my core more responsive again.

Does this scenario make any sense at all? Is it wise to have one core
router with many transit (in and out) BGP sessions also act as an
access router / default gateway for several thousand servers? What is
usually the best practice here?

Thank you for your clues.


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