Router High availability design

[Aykhan]

Hi, I have a question about topology below.I understand if we have financial afford,it is good to minimize single point of failures.For example adding two router and two internet connection.Due to diagram below we have 2 links from per router: one for each distribution switches.If we had one link from per router to only one of distribition switch,we can use hsrp between two routers to have high avialibility in the case of router failure.But the thing I don't understand is in the diagram below how should I configure those routers with two links of each.I know we can't have 2 interface of same router in the same subnet.So we can't use hsrp on the same router.So what should I do with those two links on per router ?

Thanks in advance.

[Giuseppe Larosa · Accepted solution]

Hello @Aykhan ,

in your network topology you can use L3 p2p links between the edge Internet facing routers and the distribution switches at this point you can run OSPF in area 0 between R1,R2 and DS1, DS2.

With R1 and R2 inejcting a default route in OSPF if they receive one on the eBGP session with upstream provider.

Different choices are possible : a primary path via R1 or R2 with the primary router injecting a better default route with lower seed metric then the other one. Or in case you want to have load balancing R1 and R2 could inject default routes with same seed metric.

The OSPF running on the point to point links will take care of every topology change ( link failure or node failure)

The DS1 and DS2 have to advertise internal subnets in OSPF as internal routes.

In this way you don't need HSRP on any link between R1,R2 and DS1,DS2 only OSPF.

Note: in OSPF you need the following command to inject a default route in OSPF domain as an LSA type 5:

default-information originate route-map check-BGP

ip prefix-list DEFAULT permit 0.0.0.0/0

access-list 11 remark to match eBGP next-hop

access-list match host <R1-cloud1-next-hop>

route-map check-BGP permit 10

match address prefix DEFAULT

match ip next-hop 11

set metric 50

set type 1

similar on R2 here depending on the strategy the seed metric can be the same or different . Type O E1 is recommended in cases where multiple exit points (ASBR) are present in an OSPF domain.

Hope to help

Giuseppe

[Aykhan]

Hi,Giuseppe.Firstly, thank you for your time.So,I have to assign different subnet for each p2p link between DS and Router ?

[Giuseppe Larosa]

Hello @Aykhan ,

yes each p2p L3 link will have its own IP subnet.

Hope to help

Giuseppe

[Aykhan]

Sorry to bother you,can I also use floating static route instead of ospf?What is the pros and cons?

[MHM Cisco World]

two ways

1- have four L3 P2P between two edge routers and Dis SW "this solution need Dis. SW be as L3 SW"

2- have two SVI in each router and have two harp groups

[Aykhan]

Hi, can you please elaborate second way ?