Re: BGP Next-Hop

From: Victor Cappuccio (vcappuccio@gmail.com)
Date: Fri Nov 23 2007 - 13:09:16 ART

in adition to that, If the receiving BGP router is in the same subnet as the
current next-hop address, the next-hop address remains unchanged.
R2(config)#router bgp 2
R2(config-router)#neigh 1.2.123.3 remote-as 3
R2(config-router)#neigh 1.2.123.1 remote-as 1
R2(config-router)#do show frame-relay map
Serial0/0/0 (up): ip 1.1.123.3 dlci 101(0x65,0x1850), dynamic,
              broadcast,, status defined, active
Serial0/0/0 (up): ip 192.168.31.2 dlci 201(0xC9,0x3090), dynamic,
              broadcast,, status defined, active
Serial0/0/0 (up): ip 1.2.123.1 dlci 100(0x64,0x1840), dynamic,
              broadcast,, status defined, active

Enter configuration commands, one per line. End with CNTL/Z.
R1(config)#router bgp 1
R1(config-router)#neigh 1.2.123.2 remote-as 2
R1(config-router)#net 6.6.6.0 mask 255.255.255.0
R1(config-router)#int lo0
R1(config-if)#ip add 6.6.6.
*Nov 23 16:46:39.631: %LINEPROTO-5-UPDOWN: Line protocol on Interface
Loopback0,
 changed state to up
R1(config-if)#ip add 6.6.6.6 255.255.255.0

R2#show ip bgp | b Net
   Network Next Hop Metric LocPrf Weight Path
*> 6.6.6.0/24 1.2.123.1 0 0 1 i

R3#show ip bgp
BGP table version is 2, local router ID is 1.2.123.3
Status codes: s suppressed, d damped, h history, * valid, > best, i -
internal,
              r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete

   Network Next Hop Metric LocPrf Weight Path
*> 6.6.6.0/24 1.2.123.1 0 2 1 i
R3#

So I think that the posible solution if you are not allowed to do the
frame-relay mappings to R1, could be

R3#conf te
Enter configuration commands, one per line. End with CNTL/Z.
R3(config-route-map)#set ip next-hop 1.2.123.2
R3(config-route-map)#exit
R3(config)#router bgp 3
R3(config-router)#neigh 1.2.123.2 route-map SETNH in
R3(config-router)#do clear ip bgp * in
R3(config-router)#do show ip bgp
BGP table version is 3, local router ID is 1.2.123.3
Status codes: s suppressed, d damped, h history, * valid, > best, i -
internal,
              r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete

   Network Next Hop Metric LocPrf Weight Path
*> 6.6.6.0/24 1.2.123.2 0 2 1 i

So now we go to the HUB :)

Thanks 

-- 
Victor Cappuccio
www.vcappuccio.wordpress.com

On Nov 23, 2007 4:50 PM, Hash!!! <hashng@gmail.com> wrote:

> Gupta,
>
> You will need to have the basic IP reachability for BGP peering sessions
> to
> be established, check your frame relay configuration first and make sure
> you
> can ping from spoke to spoke.
>
> HTH
>
> Hash
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> Gupta, Gopal (NWCC)
> Sent: Friday, November 23, 2007 6:26 PM
> To: Salau, Yemi; Victor Cappuccio
> Cc: Cisco certification
> Subject: RE: BGP Next-Hop
>
>  No R1 cant ping R2/R3. I didn't define PVCs between spokes.
>
> -----Original Message-----
> From: Salau, Yemi [mailto:yemi.salau@siemens.com]
> Sent: Friday, November 23, 2007 20:48
> To: Victor Cappuccio; Gupta, Gopal (NWCC)
> Cc: Cisco certification
> Subject: RE: BGP Next-Hop
>
> Just to add to Victor's comments ...
>
> Next-hop-self is normally manually set within iBGP peers. The concept is
> that my other internal neighbor doesn't know how to get to my own
> external neighbor(can't ping it), so I'm telling him how to get there,
> using myself as the next-hop to all routes coming from my external
> neighbor.
>
> In essense, eBGP don't need next-hop-self to be manually set as this
> "should" happen within the process itself, well automatically. Hence,
> "%BGP: next-hop-self is implied for an eBGP peer, there is no need to
> configure it".
>
> If it's not happening in your scenerio, then could this be down to the
> NBMA setup? Can R1 ping R2/R3? etc.?
>
> Many Thanks
>
> Yemi Salau
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> Victor Cappuccio
> Sent: Friday, November 23, 2007 2:54 PM
> To: Gupta, Gopal (NWCC)
> Cc: Cisco certification
> Subject: Re: BGP Next-Hop
>
> Hi Gupta,
>
> is 155.1.0.1 an external neighbor in your topology :)
>
> Example:
> WG6R3(config-router)#do show ip bgp neigh 4.4.4.4 | in external BGP
> neighbor is 4.4.4.4,  remote AS 4, external link
> WG6R3(config-router)#!So you can not configure Next-Hop-Self here
> WG6R3(config-router)#neigh 4.4.4.4 next-hop-self
> %BGP: next-hop-self is implied for an eBGP peer, there is no need to
> configure it WG6R3(config-router)#do show ip bgp neigh 2.2.2.2 | in
> internal
>
> EBGP next hops shall be announced using the IGP or you must Redistribute
> connected interfaces into the IGP at the edge routers, or you must
> Include links to EBGP neighbors into the IGP and configure them as
> passive interfaces
>
> You can configure an edge router to set its IP address as the next-hop
> address even when the BGP updates are sent across IBGP sessions. As a
> result, there is no need for the receiver of the IBGP information to
> know how to reach the far end of the EBGP session, because that IP
> address is no longer set as the next hop.
> Both EBGP and IBGP sessions forward BGP updates but in slightly
> different ways. BGP attributes are not changed when an update is sent
> across an IBGP session unless next-hop-self is configured.
>
> HTH
>
> Victor Cappuccio
> www.vcappuccio.wordpress.com
>
> On Nov 23, 2007 3:03 PM, Gupta, Gopal (NWCC) <gopal.gupta@hp.com> wrote:
>
> > Hi Folks,
> >
> > I am facing issue with BGP..
> >
> > R1 , R2, R3 are spokes connected to hub R5 throgh Frame relay .... all
>
> > with the major interface.
> > having subnet 155.1.0.0/24 and all are in their own individual AS ; R1
>
> > is in AS1, R2 in 2, R3 in 3, R5 in 5.
> >
> > when routes originated by R2 are sent to R5 and then R5 in turn sends
> > that route to R3 or R1, the next hop doesn't change which should be
> > changed coz of EBGP connections and should not be changed coz of
> > Frame-relay NBMA on same subnet.
> >
> > and if i try to set next-hop-self under neighbor stement on R5 for
> > R1,R2&R3..i get an error message
> >
> > R5(config-router)#neighbor 155.1.0.1 next-hop-self
> > %BGP: next-hop-self is implied for an eBGP peer, there is no need to
> > configure it R5(config-router)#neighbor 155.1.0.2 next-hop-self
> > %BGP: next-hop-self is implied for an eBGP peer, there is no need to
> > configure it R5(config-router)#neighbor 155.1.0.3 next-hop-self
> > %BGP: next-hop-self is implied for an eBGP peer, there is no need to
> > configure it
> >
> > I know i can set it manually throgh Route-map, is this the only way we
>
> > can have workaround or i am missing something.....not sure.
> >
> > Any Comments please !!!!!!
> >
> > Best Regards,
> > Gops
> >
> >
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>
>
>
> --
>
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>

-- 
Victor Cappuccio
www.vcappuccio.wordpress.com

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