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Use of the "default-address-selection" command

[ Edited ]
‎07-22-2020 04:28 AM

Hello,

 

Our goal is source all locally generated traffic from the Routing Engine (RE) of a device to use the IP address of  the loopback interface. This will concern different traffic such as traffic going from the local RE of the device to the syslog server, NTP server, SNMP server, Radius server etc. To accomplish this we plan to use the "default-address-selection" command.

 

My only concern was for point to point links where the physical interface address is used for OSPF peering. For this particular  connection instead of using the loopback address, we would want the interface address to be used, as we wouldn't be able to form OSPF peering if loopback address was used in this scenario.

 

There is also another way to source RE generated traffic for various specific protocols by using the source-address command, but this is not that efficient, as it requires us to specify the source address for each protocol.

 

Could somebody please advise on this setup?

 

 

 

Kudos are always appreciated. Please mark solution as accepted if it help solves your issue.
Thanks,
B
5 REPLIES 5
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Routing

Re: Use of the "default-address-selection" command

‎07-22-2020 04:35 AM

Hi biraj,

 

default-address-selection should not affect ospf and similar routing protocols.

 

Please mark "Accept as solution" if this answers your query.

Best Regards,

Mohamed

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Solution
Accepted by topic author biraj
‎07-27-2020 06:33 AM

Re: Use of the "default-address-selection" command

‎07-22-2020 04:38 AM

Hi,

 

OSPF should not be affected by the configuration knob "default-address-selection"

 

https://www.juniper.net/documentation/en_US/junos/topics/topic-map/tcp-configure-features.html

 

quoting from the above link 

"NOTE

For IP packets sent by IP routing protocols (including OSPF, RIP, RSVP, and the multicast protocols, but not including IS-IS), the local address selection is often constrained by the protocol specification so that the protocol operates correctly. When this constraint exists in the routing protocol, the packet's source address is unaffected by the presence of the default-address-selection statement in the configuration. For protocols in which the local address is unconstrained by the protocol specification like IBGP and multihop EBGP, if you do not configure a specific local address when configuring the protocol, the local address is chosen using the same method as other locally generated IP packets."


 

If this solves your problem, please mark this post as "Accepted Solution."I

Regards,
A.A.
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Re: Use of the "default-address-selection" command

‎07-24-2020 07:55 AM

Thanks  @. Looks like there is no issue with configuring "default-address-selection" with OSPF but with BGP we have to explicitly configure the local address, otherwise, there might be issue. Would that be a correct assumption?

Kudos are always appreciated. Please mark solution as accepted if it help solves your issue.
Thanks,
B
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Re: Use of the "default-address-selection" command

‎07-24-2020 07:59 AM

Hello,

 


@biraj wrote:

but with BGP we have to explicitly configure the local address, otherwise, there might be issue. Would that be a correct assumption?


 

No. It's a popular JUNOS misconception that "default-address-selection" influences ALL locally-generated traffic - no, it is not, the JUNOS routing protocol traffic is not affected by "default-address-selection" knob.

JUNOS BGP always uses the outgoing interface' IP address as source unless You explicitly configure "local-address".

There is no difference between iBGP and eBGP in this regard.

HTH

Thx

Alex 

 

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Re: Use of the "default-address-selection" command

‎07-27-2020 06:33 AM

Thanks 

Kudos are always appreciated. Please mark solution as accepted if it help solves your issue.
Thanks,
B
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