From: Mohamed (nmohamed@cisco.com)
Date: Wed May 05 2004 - 11:49:25 GMT-3
Hi Devi,
I checked in my routers,pls chk the config
Down---------SFM---------Side
SFM#sh ip bgp
BGP table version is 5, local router ID is 219.2.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i -
internal,
S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 100.100.100.0/24 0.0.0.0 0 32768 i
*> 200.100.100.0 25.25.25.26 156160 32768 i
*> 201.100.100.0 25.25.25.26 156160 32768 i
*> 203.1.1.0 99.99.99.2 0 300 400 ?
SFM#
SFM#
SFM#
SFM#
SFM#sh run | b router bgp
router bgp 100
no synchronization
bgp log-neighbor-changes
network 0.0.0.0
network 100.100.100.0 mask 255.255.255.0
network 200.100.100.0
network 201.100.100.0
neighbor 25.25.25.26 remote-as 100
neighbor 25.25.25.26 route-map INT out
neighbor 99.99.99.2 remote-as 300
no auto-summary
!
ip classless
no ip http server
!
!
!
!
route-map INT permit 10
set metric-type internal
!
!
!
dial-peer cor custom
!
!
!
!
line con 0
exec-timeout 35791 0
line vty 0 4
no login
transport input lat pad mop telnet rlogin udptn nasi
!
end
SFM#
In SFM I give the command set metric-type internal in the route-map to
Down router and I expect that ? Routes will be converted to IGP as you
specified,but iam not getting as IGP in Down.Pls clarify!!
Down#sh ip bgp
BGP table version is 202, local router ID is 201.100.100.100
Status codes: s suppressed, d damped, h history, * valid, > best, i -
internal
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*>i100.100.100.0/24 25.25.25.25 0 100 0 i
*>i200.100.100.0 25.25.25.25 156160 100 0 i
*>i201.100.100.0 25.25.25.25 156160 100 0 i
*>i203.1.1.0 99.99.99.2 0 100 0 300 400 ?
Down#
Down#
Thanks
Mohamed.
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Devi Mallampalli
Sent: Tuesday, May 04, 2004 6:11 PM
To: Mohamed; Sergio Jimenez Arguedas; ccielab@groupstudy.com
Subject: RE: BGP MED Scenario!!!-2nd try
Hi Mohamed & Sergio ,
Let me see if I can elaborate on what I said earlier. May be any CCIE
present in the forum can validate my conceptual understanding on BGP
here.
The command "set metric-type internal" is used with in BGP context where
you want BGP to "fake" ( just like AS prepend) inbound IGP routes which
appear as "?" with in "sh ip bgp" output to "i". In otherwords , you
want BGP to make incoming "incomplete ("?") routes , i.e IGP routes to
be consider as iBGP routes which can appear as "i" with in "sh ip bgp"
output.
That makes logical sense if you think about it.
As part of BGP route selection process, "i"(iBGP) routes are preferable
to "?" routes(incomplete which are redistributed
routes) and then "?" routes are preferred to "e" (EGP routes which are
older version of BGP 4.0) routes.
So there are 2 ways to accomplish this task of converting incomplete/?
routes of IGP in to iBGP/i routes on the AS border router so that those
routes will be preferred according to the BGP route selection process.
This is true even though the IGP's route's AD is lesser(90 in case of
EIGRP) when compared to "i"/iBGP route which is 200. Because BGP table
unlike Routing table , will picking up most attractive routes in the
above said order rather based on AD or Prefix length which is the case
with Routing table.
1st method of accomplishing this is "set metric-type internal" condition
under route map and second one being "set origin" attribute. Thus if I
remember correctly , Sergio original config is correct , i.e. his Route
map is doing her job and that is why he was seeing IGP routes with "i"
sign in sh ip bgp output.
Do not worry about Multi homing scenario and I do not think LAB exam
covers such a kind of complex MED scenarios.
I think as long as we are aware MED's nature ( i.e. it is configured on
the local AS to influence the external AS) and
functionality ( i.e. defines which incoming route/interface the
external AS should take in order to come in to my AS) ,the applicable
interface ( always on outbound ) and possible scenarios , we are pretty
much safe in the MED section of the BGP in the exam , I think.
Hope I am making sense here.
Regards
Devi....
-----Original Message-----
From: Mohamed [mailto:nmohamed@cisco.com]
Sent: Tuesday, 4 May 2004 5:45 PM
To: Devi Mallampalli; 'Sergio Jimenez Arguedas'; ccielab@groupstudy.com
Subject: RE: BGP MED Scenario!!!-2nd try
Hi Devi,
Still iam not clear,I know bgp deterministic-med command,to choose the
router with the best MED. But what does set metric-type internal does is
the doubt. The explanation given in the cisco site is not that much
clear.-The cmd (set metric-type internal) in BGP will enable the MED
values on prefixes advertised to EBGP peer to match the IGP metric of
the next hop.- It is also confusing when you say "If this command is
used, multiple BGP speakers in a common autonomous system can advertise
different MED values" In an AS how can multiple BGP speakers advertise
diff MED values,when they use the same IGP for calculating the metrics.
Thanks for giving your time, please clarify us more.
Thanks
Mohamed.
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Devi Mallampalli
Sent: Tuesday, May 04, 2004 9:49 AM
To: Sergio Jimenez Arguedas; ccielab@groupstudy.com
Subject: RE: BGP MED Scenario!!!-2nd try
Hi Sergio,
When you originate a BGP route sourced from an IGP , then IGP's metric
is converted to BGP MED by default. However if the route is local to the
router the MED is by default "0" when you inject that route in to EBGP.
The cmd (set metric-type internal) in BGP will enable the MED values on
prefixes advertised to EBGP peer to match the IGP metric of the next
hop. If this command is used, multiple BGP speakers in a common
autonomous system can advertise different MED values ( If multihoming
with multiple ISPs and peering with one ISP at multiple points, use "bgp
deterministic-med" and enable it on all routers in the AS . And this
will ensure the comparison of "MED variable" when choosing routes
advertised by different peers in the same AS)for a particular prefix.
Also, note that if the IGP metric changes, BGP will readvertise the
route every 10 minutes.
Hope this helps in terms of what this command does in BGP.
Regards
Devi.
-----Original Message-----
From: Sergio Jimenez Arguedas [mailto:sejimenez@its.co.cr]
Sent: Tuesday, 4 May 2004 4:45 AM
To: ccielab@groupstudy.com
Subject: Fw: BGP MED Scenario!!!-2nd try
Hi Devi,
I agree with you, but the doubt is the following:
___________________________________
Hi,
Mohamed, I really did it, but WITHOUT the route-map INT SFM Tx the
prefix to Side with the eigrp metric.
So, I got confused with that cmd (set metric-type internal) in BGP.
___________________________________
Thanks for your time!!!
Sergio
----- Original Message -----
From: "Devi Mallampalli" <Devi.Mallampalli@chubb.com.au>
To: "Mohamed" <nmohamed@cisco.com>; <ccielab@groupstudy.com>
Sent: Monday, May 03, 2004 7:25 AM
Subject: RE: BGP MED Scenario!!!-2nd try
> Hi Sergio & Mohamed,
>
> Let me understand this me being a late comer/listener to this Hi,
> >
> > Mohamed, I really did it, but WITHOUT the route-map INT SFM Tx the
> > prefix to Side with the eigrp metric.
> >
> > So, I got confused with that cmd (set metric-type internal) in BGP.
> conversation.
>
> Down---------------SFM-----------Side---------Up . In this topology,
> Down and SFM are running "eigrp" between them and SFM and "side" are
> running BGP between them. And you are "not" redistributing IGP in to
> Side from SFM and instead you want to publish the "inbound" IGP
> networks from Down to SFM in to the "BGP" Process at SFM. And you want
> to EIGRP routes of 200.100.100.0/24 appear at "side" as internal
> routes with the help of Router-maps & internal metric types.
>
> This is the scenario , right ?
>
> Honestly speaking with my very limited knowledge of BGP, I did not
> come across manipulating routes with the help of "metric-type"
> internal. Indeed I was in impression this kind of "metric-external
> types" (Type 1 and type 2) feature is more to do with "OSPF" when you
> want to influence incoming external routes from ASBR.
>
> But when you look at your below config & outputs , I kind of agree
> with Mohamed that the route map is doing what she is suppose to do and
> as result on "side " you are indeed seeing the "inbound" eigrp route
> as IGP ( "I")
>
> 200.100.100.0 99.99.99.1 128512 0 100 I >>>>
>
> Am I thinking on right lines here ? Please elaborate the issue if you
> can.
>
> On another note from LAB exam point of view , Determining the BGP
> filtering policy (what do you want to do or what author wants to
> achieve) is more critical along with which router or interface to
> apply the policy on and the configuration part is relatively easier.
> personally speaking, I try to be little cautious in getting what the
> policy should be based on the question and more importantly where to
> apply the BGP's knobs & twiddles ( ex: AS Path prepending is always
> "out" , "community is always "out" , MED is always "out" , Local
> Preference is always "In" and Weight is always "out"...etc) as it is
> very easy to commit a mistake.
>
> Regards
>
> Devi....
>
> -----Original Message-----
> From: Mohamed [mailto:nmohamed@cisco.com]
> Sent: Monday, 3 May 2004 7:05 PM
> To: ccielab@groupstudy.com
> Subject: RE: BGP MED Scenario!!!-2nd try
>
>
> Hi all,
>
> 2nd try, can anyone help on this!!
>
> Thanks
> Mohamed.
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> Of Sergio Jimenez Arguedas
> Sent: Friday, April 30, 2004 8:35 PM
> To: ccielab@groupstudy.com
> Subject: Fw: BGP MED Scenario!!!
>
>
> Hi Group
>
> Is someone able to help us, please?
>
>
> Rgds,
>
> Sergio Jiminez A.
>
>
> ----- Original Message -----
> From: "Mohamed" <nmohamed@cisco.com>
> To: "'Sergio Jimenez Arguedas'" <sejimenez@its.co.cr>;
> <ccielab@groupstudy.com>
> Sent: Friday, April 30, 2004 12:10 AM
> Subject: RE: BGP MED Scenario!!!
>
>
> > Hi,
> > Sergio,
> > Yeah, really I also don't know,hope someone would be able to help
> > us..
> >
> >
> > Thanks
> > Mohamed.
> >
> >
> >
> > -----Original Message-----
> > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> > Of Sergio Jimenez Arguedas
> > Sent: Thursday, April 29, 2004 8:27 PM
> > To: ccielab@groupstudy.com
> > Subject: Fw: BGP MED Scenario!!!
> >
> >
> >> >
> > Thanks,
> > Sergio
> >
> >
> > ----- Original Message -----
> > From: "Mohamed" <nmohamed@cisco.com>
> > To: "'Sergio Jimenez Arguedas'" <sejimenez@its.co.cr>;
> > <ccielab@groupstudy.com>
> > Sent: Thursday, April 29, 2004 12:56 AM
> > Subject: RE: BGP MED Scenario!!!
> >
> >
> > > Hi,
> > > I got your question, sorry I couldnot spare time to do in OSPF!.
> > >
> > > SFM#sh ip route eigrp
> > > 20.0.0.0/24 is subnetted, 1 subnets
> > > D 20.1.1.0 [90/28416] via 25.25.25.26, 00:01:31,
> FastEthernet3/6
> > > 200.100.100.0/24 is variably subnetted, 2 subnets, 2 masks
> > > D 200.100.100.0/24
> > > [90/128512] via 25.25.25.26, 00:01:31, FastEthernet3/6
> > > 201.100.100.0/24 is variably subnetted, 2 subnets, 2 masks
> > > D 201.100.100.0/24
> > > [90/128512] via 25.25.25.26, 00:01:31, FastEthernet3/6
> > >
> > > Note the metric on eigrp route-128512 for network 200.100.100.0/24
> > >
> > > Now -
> > > SFM#sh run | b router bgp
> > > router bgp 100
> > > no synchronization
> > > bgp log-neighbor-changes
> > > network 200.100.100.0 <<<<<<<<<<<<<<<<
> > > network 201.100.100.0 <<<<<<<<<<<<<<<<<
> > > neighbor 25.25.25.26 remote-as 100
> > > neighbor 99.99.99.2 remote-as 300
> > > neighbor 99.99.99.2 route-map INT out
> > > no auto-summary
> > >
> > > So here iam advertising network 200.100.100.0.
> > >
> > > Down---------------SFM-----------Side---------Up
> > >
> > > From down to sfm router,I run eigrp and down advertise
> > > 200.100.100.0
>
> > > and 201.100.100.0 as eigrp routes to sfm router. I DON'T
> > > REDISTRIBUTE EIGRP HERE!!!! In SFM. I advertise using network
> > > command.I set a route-map to Side router. Now see what the
> > > route-map
>
> > > is
> > >
> > >
> > > ip as-path access-list 9 permit .*
> > > route-map INT permit 10
> > > match as-path 9
> > > set metric-type internal
> > > End
> > >
> > >
> > > So BGP set the metric of the advertised routes 200.100.100.0 and
> > > 201.100.100.0 to Side as Eigrp metric=128512 . Side#sh ip bgp BGP>
> > table version is 78, local router ID is 213.1.4.1 Status codes: s
> > > suppressed, d damped, h history, * valid, > best, i - internal
> > > Origin codes: i - IGP, e - EGP, ? - incomplete
> > >
> > > Network Next Hop Metric LocPrf Weight Path
> > > *> 200.100.100.0 99.99.99.1 128512 0 100 i
> > > *> 201.100.100.0 99.99.99.1 128512 0 100 i
> > > Side#
> > >
> > > I think it don't do anyother job than this!!
> > >
> > > Thanks
> > > Mohamed.
> > >
> > >
> > >
> > > -----Original Message-----
> > > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On
> > > Behalf
>
> > > Of Sergio Jimenez Arguedas
> > > Sent: Wednesday, April 28, 2004 10:08 PM
> > > To: ccielab@groupstudy.com
> > > Subject: Fw: BGP MED Scenario!!!
> > >
> > >
> > > Hi Mohamed,
> > >
> > >
> > > I really understand that, but the doubt is the following,
> > >
> > > 172.16.0.0------RA-------------RB-------------RC-------------RD
> > >
> > >
> > > Config RB
> > >
> > >
> > > router bgp 1
> > > netw 172.16.0.0
> > > neighbor x.x.x.x remote-as 2
> > >
> > >
> > > RBsi
> > > Tx the prefix if it has a route of 172.16.0.0 in the routing
> > > table.
>
> > > RB Rx the route from RA by ospf, So RB tx the prefix with the IGP
> > > metric to RC without THE ROUTE-MAP with set metric-type internal.
> > >
> > >
> > > Question: How can I use a route-map with set metric-type internal?
> > >
> > >
> > > Thanks,
> > >
> > >
> > > Sergio
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > > ----- Original Message -----
> > > From: "Mohamed" <nmohamed@cisco.com>
> > > To: "'Sergio Jimenez Arguedas'" <sejimenez@its.co.cr>;
> > > <ccielab@groupstudy.com>
> > > Sent: Wednesday, April 28, 2004 1:20 AM
> > > Subject: RE: BGP MED Scenario!!!
> > >
> > >
> > > > I tried in my router,
> > > >
> > > > A----------B----------C---------D
> > > >
> > > > A,B are IBGP,running OSPF.
> > > > B redistributing OSPF into BGP.
> > > > C is EBGP of B.
> > > > D is Ebgp of C
> > > >
> > > > Now in C,we get the metrics from B,bcoz C only reset the metric
> > > > to
>
> > > > zero. In D we don't get metric.
> > > >
> > > >
> > > > Now if u put route-map and set metric-type int or even set
> > > > origin igp,I don't get any mteric in D,bcoz MED is a optional
> > > > Non-transitive attribute,which never passed to EBGP peers.
> > > >
> > > >
> > > > Thanks
> > > > Mohamed.
> > > >
> > > >
> > > >
> > > >
> > > > -----Original Message-----
> > > > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On
> > > > Behalf
> >
> > > > Of Sergio Jimenez Arguedas
> > > > Sent: Wednesday, April 28, 2004 2:29 AM
> > > > To: ccielab@groupstudy.com
> > > > Subject: BGP MED Scenario!!!
> > > >
> > > >
> > > > Hi Group,
> > > >
> > > > I have a question about BGP MED, the scenario is the following:
> > > >
> > > >
> > > >
> > > > --------------EB GP----------------------R4
> > > > OSPF |
> > > > |ibgp
> > > > NETA
> > > > ----------R1------------------------------R2------------EBGP----
> > > > --
> > > > --
> > > > --
> > > > --
> > > > -----
> > > > -----R3-------------EBGP-----------------R5
> > > >
> > > >
> > > > R1 Tx NETA to R2 by OSPF and R2 Tx NetA to R3/R4 by EBGP. R3 and
> > > > R4 Rx
> > >
> > > > NETA with the IGP (OSPF) metric. When R3 Tx the route R5, R5 Rx
> > > > the route with the metric 0. I understood it, but I have the
> > > > following
> > > > question:
> > > >
> > > >
> > > > If I apply a route-map from R3 to R5 with set metric-type
> > > > internal.......This would cause BGP routes to carry the internal
> > > > IGP
> >
> > > > metric as the BGP MED?
> > > >
> > > > R3/R4 carried the IGP metric without a route-map in R2.
> > > >
> > > >
> > > >
> > > > Could you help me, please?
> > > >
> > > >
> > > > Reference: HALABI Pag_340
> > > >
> > > >
> > > >
> > > > Rgds,
> > > >
> > > >
> > > > Sergio Jiminez A.
> > > >
> > > > ________________________________________________________________
> > > > __
> > > > __
> > > > __
> > > > _
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