From: cebuano (cebu2ccie@cox.net)
Date: Thu Jan 16 2003 - 13:34:03 GMT-3
Dave,
If you look at the explanation on this page
http://www.cisco.com/univercd/cc/td/doc/cisintwk/ics/icsbgp4.htm#xtocid2
043950
It says, " Turning off synchronization on Router A will cause Router A
to advertise network 203.250.15.0. This step is required because Router
A will not synchronize with OSPF BECAUSE OF MASK DIFFERENCES. For the
same reason, synchronization should also be turned off on Router B so
that it can advertise network 203.250.13.0."
So I changed the link between RtrB and RtrF to 203.250.15.0/24 to match
that between RtrA nad RtrF of 203.250.14.0/24. I then turn
synchronization ON.
Again, this prevents both RtrA and B from advertising iBGP-learned
routes to their eBGP peers.
So two things...
1) The subnet mask difference has NOTHING to do with synchronization
(unless this was true in older IOS releases).
2) I thought that it's okay to leave synchronization on since in this
scenario the eBGP routes are being redistributed into OSPF thus RtrF in
between RtrA&B have IGP knowledge of these eBGP routes.
What am I missing?
Elmer
-----Original Message-----
From: MADMAN [mailto:dave@interprise.com]
Sent: Thursday, January 16, 2003 6:52 AM
To: cebuano
Cc: ccielab@groupstudy.com
Subject: Re: BGP Synchronization Rule - changed in 12.0??
Check out this URL:
http://www.cisco.com/en/US/customer/tech/tk648/tk365/technologies_tech_n
ote09186a0080094431.shtml
Also as of 12.2.8, If I recall correctly, it may be 8T,
synchronization is disabled by default finally!!
Dave
cebuano wrote:
> After reading the Practical Design pages, I missed this very important
> paragraph...
>
http://www.cisco.com/univercd/cc/td/doc/cisintwk/ics/icsbgp4.htm#xtocid2
> 043950
>
> Turning off synchronization on Router A will cause Router A to
advertise
> network 203.250.15.0. This step is required because Router A will not
> synchronize with OSPF because of mask differences. For the same
reason,
> synchronization should also be turned off on Router B so that it can
> advertise network 203.250.13.0.
>
> So, does anyone have a link that I can look up as to why the different
> Masks will cause problems with Synchronization?
>
> TIA.
> Elmer
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
> Joe Chang
> Sent: Wednesday, January 15, 2003 5:53 PM
> To: ccielab@groupstudy.com
> Subject: Re: BGP Synchronization Rule - changed in 12.0??
>
> Cebuano wrote:
>
>>My question is this.if synchronization is turned ON (default).even if
>>the BGP routes are learned via OSPF.BGP does not install them in its
>>routing table. Is this how synchronization affects iBGP peer
>>advertisements?
>
>
> I think in this case the rule of synchronization still holds because
the
> BGP
> routes A is advertising have been successfully installed in the BGP
> table of
> B. The routing table (which is a separate entity from the BGP table,
of
> course) does not install the BGP routes because of the lower AD of
OSPF
> (which you have already discovered in your second example). In other
> words,
> what you observed is not a failure of synchronization because a
> successful
> update of the BGP table does not necessarily mean the routing table
must
> also reflect that update. In your first example router B should be
able
> to
> advertise its IBGP routes to the external AS.
> .
> .
-- David Madland CCIE# 2016 Sr. Network Engineer Qwest Communications 612-664-3367"You don't make the poor richer by making the rich poorer." --Winston Churchill .
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