Re: BGP Unsuppress map

Garth,

*Sorry for the long post and typos if there are any.*

* *

*Lets say you have the following topology:*

*R1* (f0/0 = 10.1.1.1/24) ---------------------------------- (f0/0 =
10.1.1.2/24) *R2*

R1s Lo0 = 100.1.0.1/24

R1s Lo0 = 100.1.1.1/24

R1s Lo0 = 100.1.2.1/24

R1s Lo0 = 100.1.3.1/24

*R1 is advertising its Loopback interfaces in BGP; here is the configuration
of R1 and R2:*

*On R1*

*R1#Show run | S router bgp *

* *

router bgp 100

 no synchronization

 bgp log-neighbor-changes

* network 100.1.0.0 mask 255.255.255.0*

* network 100.1.1.0 mask 255.255.255.0*

* network 100.1.2.0 mask 255.255.255.0*

* network 100.1.3.0 mask 255.255.255.0*

 neighbor 10.1.1.2 remote-as 200

 no auto-summary

*On R2*

*R2#Sh run | S router bgp*

* *

router bgp 200

 no synchronization

 bgp log-neighbor-changes

 neighbor 10.1.1.1 remote-as 100

 no auto-summary

*NowR1 needs to summarize (Aggregate) its Loopback interfaces:*

*On R1*

R1(config)#router bgp 100

R1(config-router)#*aggregate-address 100.1.0.0 255.255.252.0*

**

*To verify:*

* *

*On R2*

*R2#Show ip bgp | B Net*

* *

   Network Next Hop Metric LocPrf Weight Path

**> 100.1.0.0/24 10.1.1.1 0 0 100 i***

**> 100.1.0.0/22 10.1.1.1 0 0 100 i***

**> 100.1.1.0/24 10.1.1.1 0 0 100 i*

**> 100.1.2.0/24 10.1.1.1 0 0 100 i*

**> 100.1.3.0/24 10.1.1.1 0 0 100 i***

*Note by default when we aggregate in BGP the aggregate + all the specific
routes are advertised, there are few ways to suppress a specific prefix(s)
and advertise the aggregate ONLY; one way to suppress all the specific
routes is to use the Summary-only keyword:*

*On R1*

R1(config)#router bgp 100

R1(config-router)#*aggregate-address 100.1.0.0 255.255.252.0* *summary-only*

*To verify:*

* *

*On R2*

*R2#Show ip bgp | B Net*

* *

   Network Next Hop Metric LocPrf Weight Path

**> 100.1.0.0/22 10.1.1.1 0 0 100 i***

*Note the output of the above show command reveals that the summary-only
keyword suppressed all the specific routes and advertised the aggregate
ONLY; this can be seen on R1 as well:*

*On R1*

*R1#Show ip bgp | Inc s*

* *

BGP table version is 10, local router ID is 100.1.3.1

Status codes: s suppressed, d damped, h history, * valid, > best, i -
internal,

Origin codes: i - IGP, e - EGP, ? - incomplete

*s>* 100.1.0.0/24 0.0.0.0 0 32768 i

*s>* 100.1.1.0/24 0.0.0.0 0 32768 i

*s>* 100.1.2.0/24 0.0.0.0 0 32768 i

*s>* 100.1.3.0/24 0.0.0.0 0 32768 i

*The letter s to the left of the prefixes identifies the prefixes that are
suppressed: *

*Now.another way to suppress all the specific routes is to use a
Suppress-map:*

*On R1*

*You configure an access-list identifying the specific prefixes that need to
be suppressed:*

R1(config)#access-list *1* permit 100.1.0.0 0.0.0.255

R1(config)#access-list *1* permit 100.1.1.0 0.0.0.255

R1(config)#access-list *1* permit 100.1.2.0 0.0.0.255

R1(config)#access-list *1* permit 100.1.3.0 0.0.0.255

*A route-map is configured to reference the access-list:*

R1(config)#route-map TST permit 10

R1(config-route-map)#match ip addr *1*

*The access-list is referenced by the suppress-map keyword; note the
summary-only is no longer configured:*

R1(config)#router bgp 100

R1(config-router)#*aggregate-address 100.1.0.0 255.255.252.0* *suppress-map
TST*

R1#*cle ip bgp * out*

*To verify:*

* *

*On R2*

*Note ONLY the aggregate is advertised:*

* *

*R2#Show ip bgp | b Net*

* *

   Network Next Hop Metric LocPrf Weight Path

**> 100.1.0.0/22 10.1.1.1 0 0 100 i*

* *

*Once again, this can be seen on R1:*

*On R1*

*R1#Show ip bgp | Inc s*

* *

BGP table version is 18, local router ID is 100.1.3.1

Status codes: s suppressed, d damped, h history, * valid, > best, i -
internal,

Origin codes: i - IGP, e - EGP, ? - incomplete

*s>* 100.1.0.0/24 0.0.0.0 0 32768 i

*s>* 100.1.1.0/24 0.0.0.0 0 32768 i

*s>* 100.1.2.0/24 0.0.0.0 0 32768 i

*s>* 100.1.3.0/24 0.0.0.0 0 32768 i

*You could also manipulate the access-list to unsuppress a specific prefix
using the existing suppress-map called TST which is already applied to
the aggregate command:*

*On R1*

*To remove the existing access-list:*

R1(config)#*no* access-list 1

*Reconfiguring access-list 1 to include all the prefixes except the one that
needs to be advertised (Let's say 100.1.1.0/24): *

R1(config)#access-list 1 permit 100.1.0.0 0.0.0.255

R1(config)#access-list 1 permit 100.1.2.0 0.0.0.255

R1(config)#access-list 1 permit 100.1.3.0 0.0.0.255

* *

*Note prefix 100.1.1.0/24 is NOT included in the above access-list.*

R1#*cle ip bgp **

*On R2*

*R2#Show ip bgp | b Net*

* *

   Network Next Hop Metric LocPrf Weight Path

**> 100.1.0.0/22 10.1.1.1 0 0 100 i***

**> 100.1.1.0/24 10.1.1.1 0 0 100 i***

*Note in the above configuration we are using the suppress-map to
unsuppress a given prefix, basically what we are saying is suppress networks
100.1.0.0/24, 100.1.2.0/24, 100.1.3.0/24 ONLY, therefore, since prefix
100.1.1.0/24 is NOT included in the access-list, it will be denied
suppression and will be unsuppressed or advertised to R2.*

*Another way to unsuppress a specific prefix is to use the unsuppress-map,
I personally like the unsuppress-map because you can control what is
unsuppressed/suppressed on a per neighbor basis, here is an example of
unsuppress-map:*

*On R1*

*The following aggregate-address suppresses all the specific prefixes for
all the neighbors: *

R1(config)#router bgp 100

R1(config-router)#*aggregate-address 100.1.0.0 255.255.252.0 summary-only*

*But for neighbor 10.1.1.2, we are unsuppressing a prefix based on this
route-map called TST: *

* *

R1(config-router)#*Neighbor 10.1.1.2 unsuppress-map TST*

*The following will remove the existing access-list and route-map:*

R1(config)#*no* access-list 1

R1(config)#*no* route-map TST

*The following configures an access-list identifying prefix 100.1.1.0/24,
which needs to be unsuppressed and advertised to R2:*

R1(config)#access-list 1 permit 100.1.1.0 0.0.0.255

*A route-map is configured to reference the access-list:*

R1(config)#route-map TST permit 10

R1(config-route-map)#match ip addr 1

R1#cle ip bgp *

*To verify:*

* *

*On R2*

*R2#Show ip bgp | b Net*

* *

   Network Next Hop Metric LocPrf Weight Path

**> 100.1.0.0/22 10.1.1.1 0 0 100 i***

**> 100.1.1.0/24 10.1.1.1 0 0 100 i***

*So in this case the unsuppress-map unsuppressed prefix 100.1.1.0/24, but
in reality you suppressed the other routes; therefore, the unsuppress-map
can also be used to suppress certain routes on a per neighbor basis as well.
*

**

*I guess it all depends how you look at it. But a good way to confuse a
candidate*

* *

*So when configuring the suppress-map or unsuppress-map it all depends
how the access-list and the route-map is configured; its always good to
know your options/choices, once you know your choices, no matter how the
question is asked, you will be able to figure out the answer.*

* *

*I hope this helped a little.*

On Fri, Aug 20, 2010 at 7:32 AM, Bilal Hansrod
<bilal.hansrod_at_gmail.com>wrote:

> Good luck for such a expensive lunch:)
>
> On Fri, Aug 20, 2010 at 11:59 PM, Garth Bryden <
> hacked.the.planet.on.28.8k.dialup_at_gmail.com> wrote:
>
> > Heya!
> >
> > Thankyou for the responses!
> >
> > I actually discovered this in a lab before I posted the question, then
> went
> > back and played around a bit with very similar to your examples as you
> have
> > suggested here and yup as soon as I enabled the unsuppress map on the
> > neighbor that I had the filtered routes for my router began advertising
> all
> > the routes that were aggregated AND the filtered routers :-)
> >
> > Ended up specifically denying the routes I wanted filtered from being
> > matched in the unsuppress map and solved my problem :-)
> >
> > Anyhoo I must sleep now, I have a catch a flight to sydney tomorrow so I
> > can
> > have my $1500US lunch on monday ;-)
> >
> > Cheers,
> >
> > Garth
> >
> >
> >
> > On Fri, Aug 20, 2010 at 7:41 PM, Carlos G Mendioroz <tron_at_huapi.ba.ar
> > >wrote:
> >
> > > Based only on the feature name, I would be surprised of the behaviour
> > > you describe. I would think this is a bug.
> > >
> > > Do you have a small config set that shows this ?
> > >
> > > -Carlos
> > >
> > > Garth Bryden @ 20/8/2010 6:49 -0300 dixit:
> > >
> > >> Hello,
> > >>
> > >> I was previously under the impression that an un-suppress map was used
> > to
> > >> unsuppress routes suppressed by aggregates but now my view of this has
> > >> changed, i was just wondering if I can get some clarification.
> > >>
> > >> I now believe an unsuppress map will unsuppress ANY routes that have
> > been
> > >> suppressed in any way, eg if you configure a route map to filter
> certain
> > >> routes then a unsuppress map the filtered routes will be advertised
> > again?
> > >>
> > >> Anyone else seen this behavior?
> > >>
> > >> Thanks,
> > >>
> > >> Garth
> > >>
> > >>
> > >> Blogs and organic groups at http://www.ccie.net
> > >>
> > >>
> _______________________________________________________________________
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> > >>
> > >>
> > >>
> > >>
> > >>
> > >>
> > >>
> > >>
> > > --
> > > Carlos G Mendioroz <tron_at_huapi.ba.ar> LW7 EQI Argentina
> >
> >
> > Blogs and organic groups at http://www.ccie.net
> >
> > _______________________________________________________________________
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>
>
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>

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