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Route summarization

M.Sultan
Spotlight
Spotlight

Hi guys

How to summarize these routes on ASBR router ? :

These routes belong to EIGRP I already redistributed to OPSF as well.

140.15.0.0 255.255.0.0

140.16.0.0 255.255.0.0

140.16.0.0 255.255.0.0

140.17.0.0 255.255.0.0

When i summarized on ASBR

#Router ospf 1

#summary-address 140.15.0.0 255.252.0.0

on the other router in OSPF It has All routes and new summarized route 140.14.0.0 

Although i enterd

#Clear ip ospf process #clear ip eigrp neighbours

but no changes made.

 

3 Accepted Solutions

Accepted Solutions

Harold Ritter
Cisco Employee
Cisco Employee

Hi @M.Sultan ,

140.15.0.0 is not a subnet address for a 255.252.0.0 mask. The

summary-address 140.12.0.0 255.252.0.0

statement will be generated by IOS instead.

It means that 140.12.0.0/16, 140.13.0.0/16, 140.14.0.0/16 and 140.15.0.0/16 will be summarized by this statement. 140.16.0.0/16 and 140.17.0.0/16 will not be summarized.

Regards,

Harold Ritter
Sr Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México

View solution in original post

 

this summary address not cover all subnet this make your router advertise summary and subnet that not cover by summary let start

 

summary-address 140.-0.0.0 255.240.0.0

140.15.0.0 255.255.0.0 <<- include 

140.16.0.0 255.255.0.0 <<- NOT include

140.16.0.0 255.255.0.0<<- NOT include

140.17.0.0 255.255.0.0<<- NOT include


Screenshot (439).png

summary-address 140.0.0.0 255.224.0.0

140.15.0.0 255.255.0.0 <<- include 

140.16.0.0 255.255.0.0 <<- include 

140.16.0.0 255.255.0.0<<- include 

140.17.0.0 255.255.0.0<<- include 

Screenshot (440).png

summary-address 140.12.0.0 255.252.0.0

140.15.0.0 255.255.0.0 <<- include 

140.16.0.0 255.255.0.0 <<- NOT include

140.16.0.0 255.255.0.0<<- NOT include

140.17.0.0 255.255.0.0<<- NOT include

Screenshot (441).png

View solution in original post

Hi @M.Sultan ,

You could summarize 140.16/16 to 140.19/16 using 140.16.0.0 255.252.0.0, but 140.15/16 will not be included in the summary.

Regards,

Harold Ritter
Sr Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México

View solution in original post

12 Replies 12

Harold Ritter
Cisco Employee
Cisco Employee

Hi @M.Sultan ,

140.15.0.0 is not a subnet address for a 255.252.0.0 mask. The

summary-address 140.12.0.0 255.252.0.0

statement will be generated by IOS instead.

It means that 140.12.0.0/16, 140.13.0.0/16, 140.14.0.0/16 and 140.15.0.0/16 will be summarized by this statement. 140.16.0.0/16 and 140.17.0.0/16 will not be summarized.

Regards,

Harold Ritter
Sr Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México

Thank you, but i don't want to include 140.12.0.0 the subnets my router has 140.15-16-17-18 but now the summary is taken started from 140.12.0.0.

Hi @M.Sultan ,

You could summarize 140.16/16 to 140.19/16 using 140.16.0.0 255.252.0.0, but 140.15/16 will not be included in the summary.

Regards,

Harold Ritter
Sr Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México

For 15..18, and nothing else, you can only aggregate 16 & 17, as earlier noted by @paul driver .

If it helps any, remember, address aggregation is performed along the same address blocks for the prefix, i.e. the "right" number of consecutive IPs won't always work.

For example:

192.168.1.0/31 comprises 192.168.1.0 and 192.168.1.1

and

192.168.1.2/31 comprises 192.168.1.2 and 192.168.1.3

but 

192.168.1.1 and 192.168.1.2 cannot be in the same /31.

192.168.1.1/31 is really 192.168.1.0/31

and

192.168.1.2/31 is really 192.168.1.2/31

Hello
Those subnets are discontiguous as such to capture all three /16 subnets you could use a single summary however this will encompass additional subnets that you may/or not own and do not need to be advertised

Summary-address 140.0.0.0 255.224.0.0 

Alternatively you could just advertise the 140.15.0.0/16 and summarize 140.16.0.0/140.17.0.0 subnets

Summary-address  140.16.0.0  255.254.0.0

Please rate and mark as an accepted solution if you have found any of the information provided useful.
This then could assist others on these forums to find a valuable answer and broadens the community’s global network.

Kind Regards
Paul

 

this summary address not cover all subnet this make your router advertise summary and subnet that not cover by summary let start

 

summary-address 140.-0.0.0 255.240.0.0

140.15.0.0 255.255.0.0 <<- include 

140.16.0.0 255.255.0.0 <<- NOT include

140.16.0.0 255.255.0.0<<- NOT include

140.17.0.0 255.255.0.0<<- NOT include


Screenshot (439).png

summary-address 140.0.0.0 255.224.0.0

140.15.0.0 255.255.0.0 <<- include 

140.16.0.0 255.255.0.0 <<- include 

140.16.0.0 255.255.0.0<<- include 

140.17.0.0 255.255.0.0<<- include 

Screenshot (440).png

summary-address 140.12.0.0 255.252.0.0

140.15.0.0 255.255.0.0 <<- include 

140.16.0.0 255.255.0.0 <<- NOT include

140.16.0.0 255.255.0.0<<- NOT include

140.17.0.0 255.255.0.0<<- NOT include

Screenshot (441).png

Thank you friend very clear example i understand, it is same as suppernetting FLSM subnets should start on fixed lenght.

Joseph W. Doherty
Hall of Fame
Hall of Fame

Are your network prefixes, as posted, correct?  I ask since .16. is listed twice.

As the other posters have already noted, those 3 prefixes cannot be summarized into a single prefix, unless you want to summarize .0. through .31.

Lastly, I recall (???) the OSPF summary-address is to summarize non area zero topology prefixes going to area zero on an ABR.  I.e., might not apply to external prefixes.  If true, you might need to aggregate such prefixes as part of EIGRP redistribution into OSPF.

Hi @Joseph W. Doherty ,

summary-address

is used to summarize routes redistributed into OSPF (ASBR).

area x range 

is used to summarize routes between areas (ABR).

Regards,

Harold Ritter
Sr Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México

@Harold Ritter thanks for correcting my faulty recollection.  I did confuse the ABR summary syntax with the ASBR summary syntax.

M.Sultan
Spotlight
Spotlight

On ASBR router

 

#router ospf 1

#summary-address x.x.x.x x.x.x.x


On ABR router

 

#router ospf 1

#area 0 range x.x.x.x x.x.x.x

remember summarizing routes on ASBR only works if you have do the redistribution among eigrp and ospf domains.

#summary-address x.x.x.x x.x.x.x only summarized the redistributed routes.
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