Re: [Idr] draft-litkowski-idr-flowspec-interfaceset => NLRI vs EXTCT (part 2)

["Acee Lindem (acee)" <[e-mail]>]

What was the reason for not making the interface-group part a new component type in the NLRI? It seems that making it just another Flow Spec match condition would  handle all these situations naturally.

 I remember that this was discussed but don’t recall whether it was backward compatibility or that the semantics of interface group-id was a better fit for an extended community.

Thanks,
Acee

From: Idr <[e-mail]<mailto:[e-mail]>> on behalf of Robert Raszuk <[e-mail]<mailto:[e-mail]>>
Date: Friday, July 28, 2017 at 7:52 AM
To: "Juan Alcaide (jalcaide)" <[e-mail]<mailto:[e-mail]>>
Cc: IDR List <[e-mail]<mailto:[e-mail]>>
Subject: Re: [Idr] draft-litkowski-idr-flowspec-interfaceset => NLRI vs EXTCT (part 2)

Hi Juan,

(group-id: what to you specify in ext-community; interface-group: what you specify under interface configuration)

​Obvious. ​

If you use ADD-PATHS, you can send identical NLRIs and you consider them as valid (no implicit withdraw)

​If your controller or management station does not support ADD-PATHS this is not the case. Only when you have ADD-PATHS everywhere you may play that game.

Remember flow-spec was designed to be a DDoS mitigation tool across ASes. Across ASes last time I checked deployment of ADD-PATHS is zero. Now since some folks turned it into config push ​is not something original 5575 can be blamed for.

There is a requirement that the same flowspec rule, could be used for 2 different interface-groups (let's say interfaces customer-facing and interfaces provider-facing). But also you may want to use different actions based on the group-id (section 8 of the draft)

​That is just operational mess. To do that you can use SAFI 134 where 8 octet RD is part of the NLRI what makes NLRI unique.

I think we basically need to expand/clarify the ADD-PATHS part. Regarding your points:
1. For a given NLRI, we change group-ids or actions based on what we want to achieve. So it's based on how customer sets the rule in the controller. There may be a need to send same NLRI with 2 different sets of action+group-id

​I think doing this in such way is very messy. Pushing FS routes with RD as indicated above is much cleaner if there such need to apply different actions or group IDs for the same NLRIs. ​

2. If receiver receives more than one group-id, it should apply all the actions specified to *all* the interface-group associated to all the group-ids it received. Draft does explicitly say what to do when you receive a NLRI with multiple group-ids, but I think it should be applied to all interface-groups (probably it should be clarified)

​ok.

Thx,
R.​





-J




On 7/27/2017 11:43 PM, Robert Raszuk wrote:
Juan,

Sending from single controller (single BGP peer) two updates with identical NLRIs is an implicit withdraw. ADD-PATHs has nothing to here.

Likewise RR should treat is as implicit withdraw of the previous one too.

If you go by your line of thinking what would make controller to change for given NLRI1 group-id 1 to group-id 2 if there is need to do so ?

In any case if you decide to add additional text to the current draft or decide to write new draft to address this please do make sure to clearly define two things:

1. How for a given NLRI we change either actions or group-ids

2. What should receiver do when for a given NLRI he received more then one group-id or more then one set of actions ?

Thanks,
R.





On Thu, Jul 27, 2017 at 11:37 PM, Juan Alcaide (jalcaide) <[e-mail]<mailto:[e-mail]>> wrote:
Robert,

We may support or not support unsynchronized controllers
But let's assume for a second we are just using one controller
but can a single controller sending

NLRI1 + group-id 1
NLRI1 + group-id 2

The RR receives both this routes (must be ADD-PATHS, as mentioned in the draft). The RR needs to use ADD-PATHS itself to send it to the PE (final receiver)

-J




On 7/27/2017 9:44 PM, Robert Raszuk wrote:
Hi Jakob,

Two flowspec routes with the same NLRI may be originated by different speakers.

Group-id (scoped application of specific flow-spec rules) is addressing a special case where it is generated carefully by either controller or provisioning tools. I do not see therefor a practical case where the same such rule would be coming from two or more independent sources and would be applicable ​to different interface groups.

It sounds more like a protocol conflict or provisioning bug and not something we should worry about how to carry it across RRs. Standard protocol behavior would be fine here.

Now also notice what would receiver do ... treat the subsequent update with the exactly same NLRI as implicit withdraw or run best path if they come from different peers and still apply single one to local data plane. So really there is no point to give it both such paths with ADD-PATHs. As it is on final receivers the same should be done on RRs ...

​Cheers,
//RR.​


The first route will have one group-id. The second route will have another group-id.

Thanks,
Jakob.

From: Idr [mailto:[e-mail]<mailto:[e-mail]>] On Behalf Of Robert Raszuk
Sent: Wednesday, July 26, 2017 4:38 PM
To: Juan Alcaide (jalcaide) <[e-mail]<mailto:[e-mail]>>
Cc: idr wg <[e-mail]<mailto:[e-mail]>>
Subject: Re: [Idr] draft-litkowski-idr-flowspec-interfaceset => NLRI vs EXTCT (part 2)

Hi Juan,

>  (we assume controller(s) may not want to send multiple ext-communities with same NLRI).

If I recall group-ids are carried in new RT format:

"This new BGP Route Target extended community is encoded as follows :

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Type (TBD)   |      0x02     |    Autonomous System Number   :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :     AS Number (cont.)         |O|I|      Group Identifier     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
"

So just like an UPDATE message of SAFI 128 may contain many RTs why would you see any
issue to carry multiple ext communities of the above format here ?

Best,
R.

On Thu, Jul 27, 2017 at 1:01 AM, Juan Alcaide (jalcaide) <[e-mail]<mailto:[e-mail]>> wrote:

Hi,

From a previous thread, I see from the that using EXTCOMM to carry group-id information the choice. Reason was that every AS could use their own the group-id (perhaps different than another AS). With this choice, ADD-PATHS must be mandatory in order to support multiple group-ids for the same flowspec rule  (we assume controller(s) may not want to send multiple ext-communities with same NLRI).

But the draft really does not describe how to use ADD-PATHS, and it does not discuss its problems:

- Usually, ADD-PATHS is used for path diversity, and implementations typically don't advertise 2 paths with the same next-hop (otherwise, we could have path explosion across multiple levels of RRs)

- If ADD-PATHS has to advertise the same NLRI with different ext-communities, one solution would be for ADD-PAHTS not advertise the same set of ext-communities. Unless, I guess, next-hops are different. Otherwise, we would have path explosion.

- Assuming the above, we should define a particular set of ADD-PATHS rules for flowspec AF. And, of course, leave the door open for future specific ADD-PATHs rules for other AFs (it would not be about path diversity anymore, but about propagating different information for forwarding purposes -imagine what we could have done with an IPv4 prefix: send the same net part as a NLRI and multiple ext-communities representing different prefix-lengths -).

- Since paths in a net are typically implemented as a list, there could be scalability problems if we ever want to support many group-ids.

My solution to simplify all these problems would be to add a discriminator on the NLRI (by defining a new dummy type for flowspec). We could still use ext-communities to actually match the NLRIs to interfaces. Similar to RD and RT usage.

Thoughts?

-J

_______________________________________________
Idr mailing list
[e-mail]<mailto:[e-mail]>
https://www.ietf.org/mailman/listinfo/idr