From: Brant I. Stevens (branto@branto.com)
Date: Thu Jan 13 2005 - 18:17:01 GMT-3
> Q2? If I prevent R4 from initiating a BGP session with R5 (eg. using an
> acl) doesn't
>
> that also stop any BGP session from forming regardless of who initiates it?
A2:
By eliminating BGP from the list of interesting traffic, that only prevents
the routers from DIALING each other because of BGP; it won't stop the
session from forming across the ISDN link. Don't use an interface ACL...
Use an ACLfor your intersting traffic.
Additionally, the link will not stay up because of BGP traffic... It
definitely sounds like this is what you want... The key words in that
question were/are:
> Ensure that the isdn link
> does not come up
>
> due to R4 trying to initiate a BGP session to R5
That screams "interesting traffic".
HTH,
Brant.
On 01/13/2005 02:03 PM, "ccie2be" <ccie2be@nyc.rr.com> wrote:
> Hey Andy,
>
> Thanks for thinking about this and sharing your thoughts.
>
> I had thought of doing something along those lines, but
>
> I ruled that out since the isdn link would still flap although less often.
>
> But, after seeing your note, I went back to re-read the pertinent
> requirements
>
> and maybe I need to re-think what needs to be done.
>
> Here's the actual requirement word for word:
>
> 6.5 The isdn link between R4 and R5 will be used primarily as a backup in
> the case that
>
> R4 loses its connection to the Frame Relay cloud. Ensure that the isdn link
> does not come up
>
> due to R4 trying to initiate a BGP session to R5.
>
> After re-reading this requirement, it clearly doesn't say anything about the
> link not flapping, but on the other
>
> hand, it does seem to contradict itself.
>
> If the link is primarily for backup and
>
> if R4 loses it's connection to the F/R cloud,
>
> shouldn't R4 initiate a connection to R5?
>
> Note the following about R4's config:
>
> ei 100 f/r int --> R4 bri0/0 ospf
>
> R4 is also mutually redist ei 100 into ospf and ospf into ei 100.
>
> Q? If R4's f/r connection goes down, doesn't ospf see that as a topology
>
> change (the ei routes redist into ospf are gone) and thus, because of the
>
> ospf demand-circuit cause R4 to bring up the isdn link?
>
> Q2? If I prevent R4 from initiating a BGP session with R5 (eg. using an
> acl) doesn't
>
> that also stop any BGP session from forming regardless of who initiates it?
>
> Regardless of what the solution turns out to be, this has certainly been an
> interesting
>
> problem.
>
> Thanks again. Tim
>
>
> ----- Original Message -----
> From: "Edwards, Andrew M" <andrew.m.edwards@boeing.com>
> To: "ccie2be" <ccie2be@nyc.rr.com>; "joshua lauer" <jslauer@hotmail.com>
> Cc: "Group Study" <ccielab@groupstudy.com>
> Sent: Thursday, January 13, 2005 1:29 PM
> Subject: RE: IE lab 15 - BGP over isdn
>
>
> Tim,
>
> Just crank your BGP timers keepalive and hold-time up. That will keep
> the link from constantly flapping. Note you want to do this on both
> sides of the peers so they negotiate the correct values during the
> ACTIVE period.
>
> Not sure of the specifics of this lab, but those are my thoughts.
>
> HTH,
> andy
>
> http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/
> fipr_c/ipcprt2/1cfbgp.htm#wp1002274
> -----------
>
> Adjusting BGP Timers
> BGP uses certain timers to control periodic activities such as the
> sending of keepalive messages and the interval after not receiving a
> keepalive message after which the Cisco IOS software declares a peer
> dead. By default, the keepalive timer is 60 seconds, and the hold-time
> timer is 180 seconds.You can adjust these timers. When a connection is
> started, BGP will negotiate the hold time with the neighbor. The smaller
> of the two hold times will be chosen. The keepalive timer is then set
> based on the negotiated hold time and the configured keepalive time.
>
> To adjust BGP timers for all neighbors, use the following command in
> router configuration mode:
>
> Command Purpose
> Router(config-router)# timers bgp keepalive holdtime
> Adjusts BGP timers for all neighbors.
>
>
>
>
>
> To adjust BTP keepalive and hold-time timers for a specific neighbor,
> use the following command in router configuration mode:
>
> Command Purpose
> Router(config-router)# neighbor [ip-address | peer-group-name] timers
> keepalive holdtime
> Sets the keepalive and hold-time timers (in seconds) for the specified
> peer or peer group.
>
>
>
>
>
>
>
> ------------------------------------------------------------------------
> --------
>
> Note The timers configured for a specific neighbor or peer group
> override the timers configured for all BGP neighbors using the timers
> bgp router configuration command.
>
>
> ------------------------------------------------------------------------
> --------
>
> To clear the timers for a BGP neighbor or peer group, use the no form of
> the neighbor timers command.
>
>
> -----Original Message-----
> From: ccie2be [mailto:ccie2be@nyc.rr.com]
> Sent: Thursday, January 13, 2005 10:03 AM
> To: joshua lauer
> Cc: Group Study
> Subject: Re: IE lab 15 - BGP over isdn
>
>
> Hey Josh,
>
> I'm already using the loopbacks of R4 and R5 for the bgp peering
> session.
>
> The problem (I think) is that per R4's route table, the isdn link is the
> best way
>
> to reach R5's loopback and vice versa.
>
> Remember also that the loopbacks of R3, R4 and R5 are advertised into
> the ospf
>
> domain and then redist into ei 100.
>
> Once redist into ei 100, the AD is 170 since they are ei 100 external
> routes.
>
> Therefore, R4 and R5 prefer to reach each other via the isdn link.
>
> I've tried adjusting the AD of these loopbacks such that R4 and R5
> prefer
>
> to reach each other via the f/r pvc between R4 and R3 but so far, no
> cigar.
>
> Whta's frustrating is that I'm not sure this is even the right approach.
>
> I also thought of configuring the dialer-list such that bgp traffic is
> NOT
>
> interesting but then BGP AS 200 wouldn't be fully meshed if the pvc
> between
>
> R3 and R5 goes down or if the pvc between R3 and R4 goes down.
>
> BTW, I also have an ospf demand-circuit configured on R4 and that's
> working -
>
> all the ospf adjacencies are established.
>
> Hmmm, it's a dilemma.
>
> But, I'm still open to suggestions.
>
> Thanks, Tim
> ----- Original Message -----
> From: "joshua lauer" <jslauer@hotmail.com>
> To: "ccie2be" <ccie2be@nyc.rr.com>
> Sent: Thursday, January 13, 2005 12:42 PM
> Subject: Re: IE lab 15 - BGP over isdn
>
>
>> according to the ospf section it appears to me demand circuit would be
>
>> configured. as far as bgp peering, if you peer the loopbacks of R4 and
>
>> R5 together does that keep the link down? those loopbacks are learned
>> by the ospf process correct? I wouldnt peer directly over the two
>> links with the interface ip's...that would definitely keep it up since
>
>> bgp would require
> a
>> constant connection via port 179. At first guess, looking at the
>> topology, that's what I would do. I dont offhand know of anyway to
>> spoof the bgp connection. Since the ospf ISDN link is being spoofed
>> already with demand circuit I would think that the loopback peering is
>
>> the way to go. If you lost wan connection between it would cause OSPF
>> to recalculate...the loopbacks would always be reachable. and your
>> peering would not go down. Also, since your are peering with
>> loopbacks, your isdn should never come up..
>>
>> jl
>>
>> jl
>> Joshua Lauer
>>
>> RHCE, MCSE, CCNA, CCDA, CCDP, CCNP, CCIP, CCSP,INFOSEC, CEH
>>
>> ----- Original Message -----
>> From: "ccie2be" <ccie2be@nyc.rr.com>
>> To: "Group Study" <ccielab@groupstudy.com>
>> Sent: Thursday, January 13, 2005 12:19 PM
>> Subject: IE lab 15 - BGP over isdn
>>
>>
>>> Hi guys,
>>>
>>> Is there a method of establishing bgp peering over isdn such that
>>>
>>> the bgp session doesn't make the isdn circuit flap?
>>>
>>> Analysis: I'm fairly sure this is because of BGP since I didn't
>>> have
> this
>>>
>>> problem prior to configuring the BGP peering between R4 and R5 but I
>
>>> haven't figured
>>>
>>> out how to prove that BGP is the cause. A show dialer only shows
>>> the cause as a packet
>>>
>>> to R5.
>>>
>>> I'm thinking that since R4 and R5 are ibgp peering via loopbacks,
>>> one
>>>
>>> possible way to solve this flapping problem is to make R4 and R5
>>>
>>> prefer to reach each other's loopback via the eigrp link
>>>
>>> between R4 and R3 instead of via ospf over the isdn link. I've been
>
>>> playing
>>>
>>> around with the distance command to do this but so far, no success.
>>>
>>> Has anyone else have this problem and figure out a way to solve it?
>>>
>>> Unfortunately, neither the SG or the forum offers any help on this.
>>>
>>> TIA, Tim
>>>
>>> ____________________________________________________________________
>>> ___
>>> Subscription information may be found at:
>>> http://www.groupstudy.com/list/CCIELab.html
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
[GroupStudy removed an attachment of type application/pkcs7-signature which had a name of smime.p7s]
This archive was generated by hypermail 2.1.4 : Wed Feb 02 2005 - 22:10:22 GMT-3