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BGP VS OSPF
A PRO\'S AND CON\'S INVESTIGATION
OSPF
Pro's
Con's
Has an entire picture of the network
Multicast Hello's have less than spectacular reliability
Can resolve multiple path questions sanely
Has poor administrative controls
Has good support for metrics and metric calculations
No support for FlapDampening [1]
Established on the network
Doesn't match the political structure of the network
BGP
Pro's
Con's
TCP based transport
Has less information about specific links within regional groups
Better administrative controls
Excellent support for FlapDampening [2]
Better support for the administrative structure of the network
Allows regional clusters to choose their own routing policy
Now an initial survey of the above would suggest that BGP is the
logical choice for the network.. but the con against it is MASSIVE
particularly when you consider that we already have these multipath
questions being asked see RGsouthern
27/07/05 DanFlett [3]: By "less information about specific links
within RGs" are we talking about redundant links? BGP isn't as good at
making use of redundant links as OSPF as far as I'm aware. What I
would like to find out is whether BGP will allow more than one AS to
represent the same address space - for example -
Node A is AS 64500, is a gateway to 10.10.255.0/24
Node B is AS 64501, is also a gateway to 10.10.255.0/24
This is contrary to the way BGP is supposed to be used, but if it is
allowable, it could be quite useful to us - it would mean we could use
OSPF in the clusters with a very simple config file, and the border
routers would run BGP to speak to the backbone and OSPF to speak to
the local cluster - again the config files would be simple.
Why do this? To avoid having to configure iBGP. BGP gets complicated
when you starting having use iBGP to specify the other eBGP speakers
in your own AS. A less complicated setup would be to simply give the
eBGP speakers on the borders of the cluster different AS numbers.
I'm not sure what sort of effect this config will have - will it
cause routing loops within a cluster and will BGP get confused if it
sees two ASes representing the same address space? It would be good to
get answers to this question...
Links:
------
[1] http://melbournewireless.org.au/?FlapDampening
[2] http://melbournewireless.org.au/?FlapDampening
[3] http://melbournewireless.org.au/?DanFlett
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