Robert,
On 25/11/2021 18:25, Robert Raszuk wrote:
Dear LSR WG,
I wanted to visualize the scenario we are so deeply discussing here.
Specifically BGP vs IGP flooding as well as applicability of RFC8679.
Below are three options comparing what it takes to distribute bad news
in BGP vs IGP. Keep in mind that only PE2 on the illustration is
interested in this bad news.
All in respect to L3VPN Option C as example of the service.
*Option 1* - Classic/ Today's design. If you simply enable BFD on IBGP
between PE1 and RR I bet we would not even be discussing anything as
things will just work well as is today.
I don't understand how BFD between PE1 and RR is going to address the
problem in hand. If PE1 goes down, RR will have to withdraw all
individual BGP prefixes advertised by PE1. Could be global internet
routes, internet in VRF is not uncommon either. With BGP per prefix
withdrawal the convergence is slow by definition. We want BGP PIC like
behavior and that is not what you have described above.
image.png
*Option 2 -* BGP recursion as discussed earlier to speed up NH down
propagation vs service route withdraw.
same as above.
image.png
Again very easy to accomplish today modulo your BGP implementation. RR1
to PE1 can be two BGP session - one with BFD one without to easily
separate the sequence of BGP events.
*Option 3* - BGP-LS from ABRs
BGP can carry pulses, but as I mentioned several times there are SP
networks that do not run MPLS and use other tunneling mechanisms. They
would not appreciate BGP only solution.
Having a solution in both IGP and BGP and let user decide which one he
wants to use seems a better approach to me.
thanks,
Peter
image.png
BGP-LS essentially is carrying those PUA/PULSES to those who need it.
In all cases RFC8679 can still protect against PE1 failure at local PLR
directing traffic to backup PE1' (not on the picture but we assume it is
there otherwise it is all moot).
And in fact local protection is the only one which can assure minimum
service disruption time.
For PUA/PULSE to get triggered by ABR all PE1 IGP neighbours must report
PE1 to be out - hence we are already limited to the local area detection
of PE1 down and local flooding.
Now imagine someone will not like to use BFD+BGP. Well that means that
IBGP will time out in 180 sec. That also means that whatever PUA/PULSE
is there it MUST "last" min 200 sec on the remote PEs.
(Also attaching pdf with the above illustration in case jpg-s are poor).
Many thx,
Robert
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