From: Olopade Olorunloba (lolopade@ipnxnigeria.net)
Date: Wed Oct 26 2005 - 20:59:11 GMT-3
Well, like you will say, some of these things are for theories.
Though, I've seen a situation in which I would have used the command
(unfortunately, I did not know the command then).
I have two POPs dual homing to the Internet. They are in the same AS but
bandwidth on the InterPOP connection is limited, so this should not be used
to carry Internet base traffic whatsoever. The POPs are also used to deliver
MPLS VPNs, hence they are VPNv4 neighbors. To ensure that Internet access is
not carried on the Inter POP site, I used the no-advertise community to stop
the advertisement from going out to the other POP on the iBGP session.
I think now that disabling the IPv4 session would have been a quicker and
faster way to achieve it.
-----Original Message-----
From: Andrew Lissitz (alissitz) [mailto:alissitz@cisco.com]
Sent: 27 October 2005 00:34
To: Olopade Olorunloba; swm@emanon.com; The Great Ryan; Cisco certification
Cc: comserv@groupstudy.com
Subject: RE: Different Command Format on BGP routing process
Hey Yall,
Please feel free to show me when you have seen other behavior besides
this.
If you disable ipv4 default behavior with the command you mention, then
you will need to create an address family for ipv4, ipv6, vpnv4, etc...
If you want to have a 'normal' ipv4 session with another bgp router, you
would need to create the ipv4 address family and then add the neighbors
etc... to this address family.
If you use this command and turn off default ipv4 behavior, and you
currently have ipv4 neighbors configured, then the configs will be
modified and placed under a ipv4 address fam for you. You do not need
to modify the configs, just enable the no bgp default ipv4 command and
you will see your config modified correctly for you.
A question for the group ...
In production or lab practices, have you seen a scenario / real world
problem that required you to turn off the default ipv4 behavior? I can
imagine if you have a pure vpnv4 network, and your PEs only speak vpnv4
with route reflectors and PEs then you could turn this off... but again,
how much memory / processing are you saving by not having this left @
the default? Perhaps the bgp scanner will run less...? Pure ipv6
environment perhaps?
What do you think group? Have you see this command needed in either
practice or production?
-----Original Message-----
From: Olopade Olorunloba [mailto:lolopade@ipnxnigeria.net]
Sent: Wednesday, October 26, 2005 6:47 PM
To: Andrew Lissitz (alissitz); swm@emanon.com; 'The Great Ryan'; 'Cisco
certification'
Cc: comserv@groupstudy.com
Subject: RE: Different Command Format on BGP routing process
On Cisco IOS where the IPv4 family does not show by the default, simply
disable default IPv4 session by giving the command no bgp default ipv4.
This will cause the IOS to now show the IPv4 session, and the operation
will be like what Scott has described here, because after adding a
neighbor, you will still need to go to the IPv4 address family to
activate it.
Regards
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Andrew Lissitz (alissitz)
Sent: 26 October 2005 18:18
To: swm@emanon.com; The Great Ryan; Cisco certification
Cc: comserv@groupstudy.com
Subject: RE: Different Command Format on BGP routing process
Nice Scott ... Thanks for the perspective on how to view the configs /
address families.
Cisco .. Confuses people?
-----Original Message-----
From: Scott Morris [mailto:swm@emanon.com]
Sent: Wednesday, October 26, 2005 1:08 PM
To: Andrew Lissitz (alissitz); 'The Great Ryan'; 'Cisco certification'
Cc: comserv@groupstudy.com
Subject: RE: Different Command Format on BGP routing process
No difference actually. IPv4 is the default address family used. Some
newer versions of the IOS automatically put the "address-family ipv4"
stuff there, I think just to avoid confusion with people using multiple
families.
In the R&S lab, the only one to be concerned with is the IPv6 address
family. In the SP lab, you may need the vpnv4 (MPLS VPNs) and/or
multicast as well.
All the address-family ipv4 part does is help to separate things so that
we
(humans) are less confused. Apparantly this hasn't been entirely
successful! (grin)
Always remember, there are two parts to the BGP configuration pieces.
Thinking of it this was (since BGP is an application not really an IP
routing protocol) will help you think things through!
There's first the "connections" piece which establishes your basic
connection to your neighbor. This will include the neighbor statement,
and update-source, remote-as, ebgp-multihop parameters and things like
that.
Then there's the RIB pieces. Each RIB is different. A single neighbor
may talk multiple RIB/update types. You may have 20 neighbors, and only
10 of them talk about IPv4 information. That's why each neighbor should
be activated in the appropriate RIBs they will share information with.
Then any filtering (RIB-based stuff) or network commands go under the
address families.
It's hard to follow when you're first getting into this MBGP stuff
because in generic, all-purpose BGP where we only run IPv4, it's all
just right there, not separated. But if we start thinking about the
pieces involved, then the address families suddenly aren't all that bad!
:)
Scott
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Andrew Lissitz (alissitz)
Sent: Wednesday, October 26, 2005 11:42 AM
To: The Great Ryan; Cisco certification
Cc: comserv@groupstudy.com
Subject: RE: Different Command Format on BGP routing process
Hey Ryan,
Afaik this command is used for inter-as mvpns (mpls vpn customers with
links in two or more ISPs).
There are different options for the different address families.
Curiosity... is this needed for a lab you are working on?
Once you type address-fam ipv4 (without a VRF at the end) you will be
working in the same default address family you have when you type router
bgp x. Now ... try getting rid of the command address-fam ipv4 ... once
you typed it, IOS really wants to keep it there. You will need to
either continue to work with this address-fam listed or remove bgp and
re-add bgp.
Strange how you can not get rid of this address-fam since it is the
default address family for bgp.
Does this answer your question Ryan?
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
The Great Ryan
Sent: Wednesday, October 26, 2005 8:20 AM
To: Cisco certification
Subject: Different Command Format on BGP routing process
Hi Group,
There is any different result if I use the following to enable BGP ?
Router(config)# router bgp 65412
Router(config-router)# neighbor 192.168.0.1 remote-as 65412
Router(config-router)# neighbor 192.168.0.1 ebgp-multihop 255
Router(config)# router bgp 65412
Router(config-router)# neighbor 192.168.0.1 remote-as 65412
Router(config-router)# address-family ipv4 Router(config-router-af)#
neighbor 192.168.0.1 activate Router(config-router-af)# neighbor
192.168.0.1 ebgp-multihop 255
I found something very interesting. the command "neighbor 192.168.0.1
next-hop-unchanged" will never display in the first format but it takes
effect when I use some show command. I'm afraid that if I write erase
the configuration and paste the configuration again, it will miss this
command.
Any have this experience before ?
Thanks !
Ryan
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