Routing

Can i use  different autonomous system number for each routing instance on a device ?

I want to run multiple bgp instances on a QFX devices in ip fabric devices among Spine/Leaf.

I want to achieve complete segregation of bgp for each bgp instance running in virtual routers with different autonomous system number.

if we define  autonomous numbers  under routing-instance routing-option heirarchy, i hope there should not be any issue ?

Please confirm.

Hello Vicky,

You can safely use different AS# for each Routing instance created.  

You can create multiple instances of BGP, IS-IS, LDP, Multicast Source Discovery Protocol (MSDP), OSPF version 2 (usually referred to simply as OSPF), OSPF version 3 (OSPFv3), Protocol Independent Multicast (PIM), RIP, RIP next generation (RIPng), and static routes by including statements at the following hierarchy levels:

• [edit routing-instances routing-instance-name protocols]

• [edit routing-instances routing-instance-name routing-options autonomous-system]

>> Only one instance of each protocol can be configured in a single routing instance.

Hello,

You can define unique ASN for each routing instance on QFX for sure. BUT

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@vicky12345 wrote:

 

I want to achieve complete segregation of bgp for each bgp instance running in virtual routers with different autonomous system number.

 

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JUNOS routing instances do not provide "complete" separation, namely - they share the same Routing Process Daemon (RPD). Which means if a crafted packet is received in one routing instance and it crashes the RPD, then ALL routing instances are affected, irrespective of their ASN.

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@vicky12345 wrote:

 

if we define  autonomous numbers  under routing-instance routing-option heirarchy, i hope there should not be any issue ?

 

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It depends what do You call an "issue".

JUNOS AS path loop detection takes into account ALL ASN configured on local router, including routing instances and logical systems.

In other words, if BGP Update is originated by routing-instance A1 whose ASN is 64512 and it then gets into routing-instance B2 whose ASN is 64513, then routing-instance B2 will detect a loop. It may or may not be a "issue" for You depending on Your plans to trombone (or not) Your traffic thru this router. 

HTH

Thx

Alex

Hello,

As you mentioned, definitely it detect loop if the routing update received on a virtual router and if it sees it own AS local AS number(defined in routing instance level inside routing-option)  in a update packet then it will detect loop and will not accept that route but as you said

"if BGP Update is originated by routing-instance A1 whose ASN is 64512 and it then gets into routing-instance B2 whose ASN is 64513, then routing-instance B2 will detect a loop"

I want to understand How it will detect loop if the update is coming from different AS number which is AS is 64512 then it should  accept update because it is not matching my AS number which is 64513.

Please correct me if i am wrong

Thanks

Hello,

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@vicky12345 wrote:

 

 

I want to understand How it will detect loop if the update is coming from different AS number which is AS is 64512 then it should  accept update because it is not matching my AS number which is 64513.

 

One more time:

- If ASN 64512 and ASN 64513 are both  configured on the same QFX box, then

- if BGP Update with AS_PATH containing 64512 is received by BGP speaker configured on this QFX box , and

- this BGP speaker is in ASN 64513, then

- this BGP speaker will detect a loop.

The reason is that JUNOS code checks for loops for ALL and ANY ASN configured on this QFX box, inside any routing istances and logical systems.

This is works as designed.

That's why I said configuring multiple ASNs inside routing instances does not provide complete routing separation.

HTH

Thx

Alex

Dear Alex,

Thanks for answering my query.

Actually in my case,it would receive BGP update in which my other routing instance locally defines AS number will present.

I can see in other vendors. i.e. Cisco uses allow-as in command with neighbor to allow device own AS in bgp update and override loop detection in BGP. I want to know ,in Junos how can accept as update in which our device AS is present.

Thanks

Hello,

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@vicky12345 wrote:

Cisco uses allow-as in command with neighbor to allow device own AS in bgp update and override loop detection in BGP. I want to know ,in Junos how can accept as update in which our device AS is present.

 

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JUNOS has the equivalent feature called "loops" with 2 flavors:

https://www.juniper.net/documentation/en_US/junos/topics/reference/configuration-statement/loops-edit-routing-options-autonomous-system.html

https://www.juniper.net/documentation/en_US/junos/topics/reference/configuration-statement/loops-edit-protocols-bgp-family.html

Their behaviour is slightly different depending on where "loops" knob is configured.

But sign of a good design is to NOT use this knob at all.

HTH

Thx

Alex

Thanks Alex.