Walter Keen wrote:
When redesigning an OSPF service provider network, (default values, with
many gig-e links). Aside from fixing link cost issues (100mbit is
treated the same as gig-e at the moment) should I look at sub-second
timers in OSPF 'ip ospf dead-timers minimal .....' Or BFD. It looks
like either would require an IOS upgrade, but I have seen lots of
discussion about bugs in BFD. This is only for core interfaces (all
cisco 7600 series). We'll be adding MPLS and iBGP on top of this after
it's completed.
Common advice seems to be to make actual link-loss detection fast, in
preference to using BFD. That said, I know some people use BFD.
Assuming you're using LAN cards, you may want to see if you can make
router links as routed rather than SVI interfaces. Though routed
interfaces are implemented internally as VLANs, presentations I saw from
Cisco claim that this:
int G7/1
ip address ...
...will detect link-loss (much) faster than this:
int Gi7/1
switchport mode access
switchport access vlan 300
int Vlan300
ip address ...
Also, the OSPF process/SPF timers (as opposed to hello timers) are
relevant for fast convergence (rather than link-loss). I did some
research recently and concluded that, with a mostly-empty OSPF table
i.e. bulk of routes in BGP, the following settings were both safe, and
considerably "better" than the defaults:
router ospf 1
ispf
nsf
timers throttle spf 10 100 5000
timers throttle lsa all 10 100 5000
timers lsa arrival 80
...again based on reading presentations from Cisco and others advice.
HTH
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