Opened 9 years ago

Closed 8 years ago

#63 closed technical (fixed)

On the use of anycast addresses for RLOCs (from Y. Rekhter's review)

Reported by: luigi@… Owned by:
Priority: major Component: draft-ietf-lisp
Severity: - Keywords:
Cc:

Description (last modified by luigi@…)

This is Comment 38

Section 8.2

Note that more than one CE router at a site can be configured with
the same IP address. In this case an RLOC is an anycast address. This
allows resilience between the CE routers. That is, if a CE router
fails, traffic is automatically routed to the other routers using the
same anycast address. However, this comes with the disadvantage where
the site cannot control the entrance point when the anycast route is
advertised out from all border routers.

The above means that at the minimum the price of resilience between
the CE routers is the inability to support traffic engineering?
Specifically, the ISP loses any influence over the choice of which ETR
should be used to reach the multi-homed enterprise.

Moreover, if CEs are xTRs and use anycast addresses, then RLOCs are
anycast addresses as well, and thus can not be topologically
significant. Thus if an enterprise is multi-homed to two (or more)
ISPs, then use of anycast addresses for CEs would require to route
such addresses as /32 throughout the whole Internet.

Also, if anycast addresses are used as RLOCs, then how would one
deal with a situation where initially both ETR1 and ETR2 advertise
10.1.1/24 and 10.1.2/24, ITR1 routes traffic for 10.1.1.1 to ETR1, but
then ETR1, while still being up, loses connectivity to 10.1.1/24?

Change History (7)

comment:1 Changed 9 years ago by luigi@…

  • Component changed from alt to draft-ietf-lisp

comment:2 Changed 9 years ago by luigi@…

  • Description modified (diff)

comment:3 Changed 8 years ago by luigi@…

  • Resolution set to fixed
  • Status changed from new to resolved

Authors replied on the mailinglist that in their opinion there is no need to make any change to the draft. Neither the original person that raised the issue nor the mailinglist stated a different opinion.

comment:4 Changed 8 years ago by luigi@…

  • Status changed from resolved to closed

comment:5 Changed 8 years ago by yakov@…

  • Resolution fixed deleted
  • Status changed from closed to reopened

The new draft still does not fully address the issue raised in this ticket. To close this ticket the authors should replace

Another disadvantage of using anycast locators is the limited advertisement
scope of /32 (or /128 for IPv6) routes.

with the following:

When more than one CE at a site is configured with the same IP
address (in which case an RLOC is an anycast address), then in
order to avoid negative implications on routing scalability (in
order to prevent carrying RLOCs as individual /32 (or /128 for
IPv6) routes throughout the whole Internet), for a given site only
CEs connected to the same ISP may be configured with the same IP
address. Thus to avoid negative implications on routing scalability
use of anycast addresses as RLOCs for CEs should be
constrained to only the CEs connected to the same ISP.

comment:6 Changed 8 years ago by terry.manderson@…

  • Resolution set to fixed
  • Status changed from reopened to resolved

The current draft (-11) text is:

Note that more than one CE router at a site can be configured with
the same IP address. In this case an RLOC is an anycast address.
This allows resilience between the CE routers. That is, if a CE
router fails, traffic is automatically routed to the other routers
using the same anycast address. However, this comes with the
disadvantage where the site cannot control the entrance point when
the anycast route is advertised out from all border routers. Another
disadvantage of using anycast locators is the limited advertisement
scope of /32 (or /128 for IPv6) routes.

Adding in sections about constraining the use of anycasted RLOCs falls in an operations document. If such a document dealing with anycasted RLOC operation comes into existence as a BCP, then the recommendation can live there.

The text above highlights the concern about ingress in anycast. I think that is sufficient in this case.

I am resolving and closing this ticket.

Terry
(co-chair)

comment:7 Changed 8 years ago by terry.manderson@…

  • Status changed from resolved to closed
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