default route flooding using summary-address/ area range command

[sarahr202]

Hi everybody

Please consider the following set-up:

R1---Rip------R2---ospf area 1---------R3--------ospf area 0-------R2

In our example,  R2 is ASBR. R2 has following table;

C 10.10.1.0/8 directly connected loopback 1

R 10.10.10.0/24   via R1

R 10.10.20.0/24  Via R2

C 199.199.199.0/24  ( connected to R3)

When I used the command"  Summary-address 0.0.0.0 0.0.0.0 " on R2( ASBR),  and  do show running-config, I get the following:

summary-address 0.0.0.0 0.0.0.0 do-no advertise.

When checked the option as :

summary-address 0.0.0.0 0.0.0.0 ?

  not-advertise  Do not advertise when translating OSPF type-7 LSA

  tag            Set tag

  <cr>

I  am unable to understand it; would someone break it down for me ?

My second question is   when i used the command :  summary -address 0.0.0.0  0.0.0.0 on ASBr, does it not summarize all the routes present in our routing table?

=======================================

Quote from my CCNP routing book

Enterprises typically use default route in two different cases;

1)   To direct remote-site routers at the edge of t he Enterprise network to send all packets towards the core ,

2) To direct traffic on all enterprise routers towards an internet-facing routers.

Engineers could achieve both of these goals by using route summarization with the area range and summary address commands.

My question is how these commands (   area x range , summary-address)can be used to flood default route in ospf domain?

Thanks and have a great weekend

[cadet alain]

Hi,

to inject a default-route in OSPF  you must use default-information originate command.

Regards.

Alain

[sarahr202]

Thank Alain

I am not cleared as to how  these commands (  area x range, summary-address )  can be used to flood default route.

.

[Kishore Chennupati · Accepted solution]

Hi sarah,

before I answer your question about  your default route query, allow me to just refresh the place of use of

(  area x range, summary-address ) 

area x range is used on ABR to summarise the individual subnets.

summary-address  is used on ASBR to summarise the external individual subnets.

Within the ospf process if you want to flood the default route you need the default-informatino originate command.

The only time you can getaway without using that command and still generate a default route is where ABR  generates a default route when you use the stub areas features.

OSPF does not support the summary-address 0.0.0.0 0.0.0.0 command. Please see the below link to support this statement.

http://www.cisco.com/en/US/docs/ios/12_3/iproute/command/reference/ip2_s3g.html#wp1041286

The way to generate a default route on a ASBR or an ABR is to use default-informatin originate.

http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094e9e.shtml#t38

Does the book specificaly say that you can use are x range and summary-address default route?

HTH

Kishore

[Marwan ALshawi · Accepted solution]

Hi sarah

to add to the above posts

the range used for LSA type 3 summarizations also known as inter area summary

for example

10.10.1.0/24 --area 10---R1---area 0 ---- R2

R1 can summarize area 10 to be seen by R2 as /8 using area     range command

while the summary-address is used by the ASBR to summarize LSAtype 5 or in the case of Not so stuby area ASBR/ABR from type 7 to 5

however default route works diffrrently in OSPF which is as describe by other posters above

also area type can inject the default route by default in some cases

hope this help

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