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BGP question

comsats
Level 1
Level 1

guys suppose we are having 10 or 20 routes on WAN router learned from EIGRP

the wan routers has 10.15.15.0/24 to 10.15.X.0/24 etc (learned from EIGRP) and if we want to advertise a router in BGP can we use

10.15.0.0/16 route rather then putting 20 routes secondly do we have to put static null route for 10.15.0.0/16 or not

thanks for looking

16 Replies 16

lamav
Level 8
Level 8

You can advertise that /16, yes. You can also suppress the advertisement of the specific prefixes.

ip route 10.15.0.0 255.255.0.0 null0

router bgp 1

aggregate-address 10.15.0.0 255.255.0.0 summary-only

HTH

Victor

Thanks for the answer now i have a question do we really have to advertise the null0 route......if eigrp connection breaks

up even then the routes would be advertised in BGP ??? am i right or wrong secondly my main question remains stands

if we dont do null0 routes would this work or not??? thanks again

In order to advertise a route into BGP, the local router must have that route in its local routing table. The null0 route is not advertising, it's putting the /16 route into the local routing table so BGP can advertise it.

Is it possible for you to summarize the routes before your MPLS router? Then your MPLS router will already have the /16 route in its routing table and you don't have to worry about creating any to null0.

Hello Comsat,

the route to null0 is not strictly required you can use

network command for each component route

+ aggregate-address for the aggregate if you want to create the aggregate

usually the static to null0 is combined with a network command that matches directly the aggregate

Hope to help

Giuseppe

Thanks guys for your help now one more and final question.......actually there are two wan routers (the quetion is not abt the second one)

i am advertising  three networks in BGP 10.4.1.0/24

10.5.1.0/24

10.6.1.0/24

the aggregation will be look like this (correct me if i am wrong)

aggregate-address 10.4.0.0 255.255.0.0 summary-only
aggregate-address 10.5.0.0 255.255.0.0 summary-only
aggregate-address 10.6.0.0 255.255.0.0 summary-only

is it correct ?

and if i want to prepend 10.6.1.0/24 (this the requirment)

so all i have to create a prefix-list and it should look like this

ip prefix-list prepend_network_to_isp seq 10 permit 10.6.0.0/16 (it shd be /16 not 24 right????)

route-map my_prepend permit 10
match ip address prefix-list prepend_network_to_isp 
set as-path prepend X.X.X

now the imp question is shd i add permit staement in the route map (like same route _map for two other as i have read that then those two will be denied)

if yes how it shd look like

guys thanks again for looking

Hello Comsats,

at list one component router per aggregate-address has to be in the BGP table

the prefix-list should match the prefix you want to be prepended

ip prefix-list tobeprepended permit 10.6.0.0/16

you need a second empty route-map block or you will send out only one prefix

You should prepend only your own AS number one or more time.

Hope to help

Giuseppe

i am advertising  three networks in BGP 10.4.1.0/24

10.5.1.0/24

10.6.1.0/24

the aggregation will be look like this (correct me if i am wrong)

aggregate-address 10.4.0.0 255.255.0.0 summary-only
aggregate-address 10.5.0.0 255.255.0.0 summary-only
aggregate-address 10.6.0.0 255.255.0.0 summary-only

As Giuseppe pointed out with the aggregate-address command you don't need a matching route in the routing table you just need at least one of the subnets of the aggregated address.

As for the above if you have 3 /24 networks why do you want to advertise them as 3 /16 summary addresses. I mean you can but is this really what you want to do eg.

10.4.0.0/16 as a summary address would be 10.4.1.0 -> 10.4.255.0, do you really want to do that ?

Jon

Jon you are right the main thing is which i cant get my head around is that i have around

70 networks 10.4.1.0 to 10.4.200.0/24 its mix actually now i am advertising in bgp

router bgp 1

neigbour X.X.X.C remote_as X route-map traffic_out out

network 10.4.1.0 mask 255.255.255.0 (its 24 not 16)

and then

aggregate-address 10.4.0.0 255.255.0.0 summary-only

!

ip prefix-list WAN_list seq 10 permit 10.4.0.0/16

route-map traffic_out permit 10

match ip address prefix-list WAN_list

This is the best i could think of

now my question is will it advertise all my 70 networks

Yes or no???

now shd i use null0 or not??? as i am getting all teh routes from IGP (all /24)

kindly guide me guys

comsats wrote:

Jon you are right the main thing is which i cant get my head around is that i have around

70 networks 10.4.1.0 to 10.4.200.0/24 its mix actually now i am advertising in bgp

router bgp 1

neigbour X.X.X.C remote_as X route-map traffic_out out

network 10.4.1.0 mask 255.255.255.0 (its 24 not 16)

and then

aggregate-address 10.4.0.0 255.255.0.0 summary-only

!

ip prefix-list WAN_list seq 10 permit 10.4.0.0/16

route-map traffic_out permit 10

match ip address prefix-list WAN_list

This is the best i could think of

now my question is will it advertise all my 70 networks

Yes or no???

now shd i use null0 or not??? as i am getting all teh routes from IGP (all /24)

kindly guide me guys

It won't advertise all 70 routes, it will advertise a summary route of 10.4.0.0/16 to EBGP peers.

Also because you are using the summary-only keyword i'm not sure what the route-map is meant to achieve because all the more specific 10.4.x.0/24 networks will not be advertised anyway.

You do not need to use Null0.

Jon

JON

       so if /16 would be summarized still ppl can reach 70 networks that what i meant to ask......as i cant add 70 network commands in BGP

what is the solution am i doing wrong or what???

task is 70 routes with 10.4.X.X /24

so i have add 10.4.1.0/24 (which is the first subnet) and then aggregating them with /16

the route-map is cuz i am using 10.4.1.0/24 in network statement under BGP so i thought to use 10.4.0.0/16 in route-map tied up with prefix-list

look i am here as i m having problem and i m unsure

what do u think

and thanks again

comsats wrote:

JON

       so if /16 would be summarized still ppl can reach 70 networks that what i meant to ask......as i cant add 70 network commands in BGP

what is the solution am i doing wrong or what???

task is 70 routes with 10.4.X.X /24

so i have add 10.4.1.0/24 (which is the first subnet) and then aggregating them with /16

the route-map is cuz i am using 10.4.1.0/24 in network statement under BGP so i thought to use 10.4.0.0/16 in route-map tied up with prefix-list

look i am here as i m having problem and i m unsure

what do u think

and thanks again

The "summary-only" keyword you are using with your aggregate address stops any individual subnets that makes up the summary address being advertised so only 10.4.0.0/16 will be advertised.

Yes, people should be able to reach all 70 networks because the summary address covers all those 70 networks but be aware it also covers a lot more than just 70 /24 networks.

Jon

Thanks JON 100 out of 100 (you deserve that) :-)

so am i doing the right thing putting 10.4.1.0/24 under BGP and doing aggregation with /16

r u happy with route-map???? does it make sence now???

comsats wrote:

Thanks JON 100 out of 100 (you deserve that) :-)

so am i doing the right thing putting 10.4.1.0/24 under BGP and doing aggregation with /16

r u happy with route-map???? does it make sence now???

I still don't think you need the route-map because your router will only advertise out the /16 summary address. However it's not doing any harm.

Jon

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