Redundancy with load sharing?

[mmorfejr]

I have two routers each connected to a different ISP. Router A acts as primary and Router B acts as secondary. Router A and Router B are not directly connected but are connected to boarders switches A and B that are interconnected. I want to use the ISPs in such a way that I will have automatic failover while at the same time being able to use them both. What is the best approach? Should I use BGP or will OSPF do?

[Giuseppe Larosa · Accepted solution]

Hello Manolito,

the answer depends on what you get from the two ISPs:

if you get only two default routes you can simply have the two border routers to generate default routes in OSPF

router ospf 10

default-information originate route-map check_BGP

ip prefix-list only-default permit 0.0.0.0/0

route-map check_BGP permit 10

match ip address prefix-list only-default

set metric 50

set metric-type 1

if you receive specific routes in BGP and you want to have knowledge of this on core switches:

build an iBGP mesh with core switches acting as RR servers for the two border routers.

Hope to help

Giuseppe

[mmorfejr]

Thanks Giuseppe.

I only have one default route for each ISPs so I think I'll just use OSPF.

By the way if my firewall is doing the NATing, and it's outside interface is connected to the Boarder switches where the border routers are also connected. Do I need to enable OSPF on the firewalls as well or will static routes do?

[Giuseppe Larosa]

Hello Manolito,

my answer was good if border routers and core switches have a common link or are in the same OSPF domain.

If firewalls are in the middle I would try to enable OSPF on them so that the OSPF default routes can flow downstream.

For example ASA supports it in release 7.1 or above

Static routes wouldn't be the same unless using object tracking on core switches that is something that may be supported or not depending on what are your core switches

Hope to help

Giuseppe