From: Godswill Oletu (oletu@inbox.lv)
Date: Mon Jul 18 2005 - 16:13:08 GMT-3
I am trying to follow your logic, but I am finding it difficult to reconcile
this line...
".....Synch is supposed to address the issue of a router in the middle of
your network which is not running IBGP and hence does not know how to get to
a particular network that your IBGP routers are aware of....."
Is that the issue that Synchronization really addressed?
I think with BGP Synchronization, when an IBGP peer gets an update for a
route from another IBGP peer, it looks into its local IGP routing table, if
that route is present, he is free to advertise it to other BGP Peers, if
otherwise, he will refrain from advertising it. In this scenerio, all
internal routers do not have to necessary run IBGP.
To fulfill the requirements of BGP Synchronization, your IGP should be aware
of all the routes in your network, so that when these routes become
available to BGP, it can accept them and send them out to external BGP
neighbors.
eg
interface fastethernet0/0
ip address 120.1.1.1 255.255.255.0
!
interface fastethernet0/1
ip address 10.1.1.1 255.255.255.0
!
ip route 50.0.0.0 255.0.0.0 120.1.1.1
!
router bgp 120
network 120.1.1.0
network 10.1.1.0
network 50.0.0.0
network 60.0.0.0
network 70.0.0.0
!
end
You see that, BGP will not advertise networks 60.0.0.0 & 70.0.0.0, because
according to the limited configuration above, there is no reference to them
in the router's routing table, but if you disable syncronization, BGP will
accept these networks and advertise them, despite the fact that none of your
routers know how to reach those networks.
You can see that, if your BGP router advertise networks 60.0.0.0 & 70.0.0.0,
there will be problem if traffic is sent to you destined for those networks,
I believe this is the very problem BGP synchronization is setup to prevent.
Others can contribute, so that we can all learn, if this is not what your
question is about, you can throw in more light.
my 0.2
Note:
There are many other methods of making routes available to your BGP router,
the network statement used above is just one of them.
---- Godswill Oletu----- Original Message ----- From: <ccie2004@excite.com> To: <ccielab@groupstudy.com> Sent: Monday, July 18, 2005 2:01 PM Subject: BGP synchronization
> Hi All, I just came up with a question on BGP which I have been asking > myself but just can't seem to get a handle on. It has to do with BGP > Synchronization. I know this has been beaten to death and newer IOS > versions have it disabled however my question is a combination of the > underlying issue that Synch is supposed to address and Best Practises. > Synch is supposed to address the issue of a router in the middle of your > network which is not running IBGP and hence does not know how to get to a > particular network that your IBGP routers are aware of. BGP Best practises > say that never redistribute your EBGP learnt routes into your interior > routing protocol. Thinking along those lines and if I am right how exactly > would you get reachability across your network. Would you use default > routes on your non-BGP speaking routers or are there any other design type > fixes that I am missing. thx > > _______________________________________________ > Join Excite! - http://www.excite.com > The most personalized portal on the Web! > > _______________________________________________________________________ > Subscription information may be found at: > http://www.groupstudy.com/list/CCIELab.html
This archive was generated by hypermail 2.1.4 : Sun Sep 04 2005 - 17:00:30 GMT-3