Failover how much complexity will it add?

Seth Mattinen sethm at rollernet.us
Mon Nov 9 11:23:41 CST 2009


adel at baklawasecrets.com wrote:
> Actually thinking about this, I still need to understand the implications of not taking a full routing table to my setup.  So what is the likely impact going to be if I take partial instead of full routing table.  Would appreciate any feedback on this.  My organisation is only looking at using BGP as a means of failover between two separate upstream ISPs.  We are not an ISP.
> 


Some Cisco L3 switches should support this fine. A 3560 or 3750 can
speak BGP and route at line rate as long as your total number of routes
will fit in its TCAM space. Ask your upstreams how big a partial feed
from them is.

 "desktop routing" template:
 The selected template optimizes the resources in
 the switch to support this level of features for
 8 routed interfaces and 1024 VLANs.

  number of unicast mac addresses:                  3K
  number of IPv4 IGMP groups + multicast routes:    1K
  number of IPv4 unicast routes:                    11K
    number of directly-connected IPv4 hosts:        3K
    number of indirect IPv4 routes:                 8K
  number of IPv4 policy based routing aces:         0.5K
  number of IPv4/MAC qos aces:                      0.5K
  number of IPv4/MAC security aces:                 1K


If you ever need IPv6 it gets smaller:

  number of unicast mac addresses:                  2K
  number of IPv4 IGMP groups + multicast routes:    1K
  number of IPv4 unicast routes:                    3K
    number of directly-connected IPv4 hosts:        2K
    number of indirect IPv4 routes:                 1K
  number of IPv6 multicast groups:                  1.125k
  number of directly-connected IPv6 addresses:      2K
  number of indirect IPv6 unicast routes:           1K
  number of IPv4 policy based routing aces:         0
  number of IPv4/MAC qos aces:                      0.5K
  number of IPv4/MAC security aces:                 1K
  number of IPv6 policy based routing aces:         0
  number of IPv6 qos aces:                          0.625k
  number of IPv6 security aces:                     0.5K


Anything in Cisco land that can hold two full tables in hardware and can
do line rate is going to be hideously expensive.

~Seth




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