[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [RRG] On the Transitionability of LISP
At 12:27 PM 8/3/2007, Christian Vogt wrote:
I do agree that, to remain reachable, upgraded edge networks would have
to use their old locator space in addition to the new ID space. What I
am concerned about are the following two problems that arise from this:
1. It defeats all of the benefits of the ID/locator split.
2. It makes reliable address resolution infeasible.
Regarding problem 1: The four main benefits envisioned for an
ID/locator split are the following.
(i) Enabling edge networks to route packets via arbitrary providers.
(ii) Reducing the network reconfiguration cost related to rehoming.
(iii) Reducing the size of the global routing table.
(iv) Reducing the update frequency of the global routing table.
Now, if an edge network is forced to maintain its old locator space in
addition to new ID space, then /none/ of (i) through (iv) will be
satisfied. On the contrary, network administration overhead will be
increased, and the global routing table will become larger.
Actually, there seem to be quite a few stages between
advertise all locators in BGP, exactly as today
advertise nothing in BGP
For example, at a later stage in deployment one could easily imagine
advertising only heavily aggregated reachability in BGP, for those
sites that have not upgraded, while using LISP (or other solutions)
for the bulk of ones traffic.
That would give significant benefit without losing connectivity from
the non-upgraded world.
Regarding problem 2: A coexistence of locators and IDs implies that the
result of address resolution depends on the location of the resolving
host: Hosts in legacy edge networks MUST obtain legacy locators, while
hosts in upgraded edge networks SHOULD obtain IDs.
This is actually somewhat harder. If hosts actually checked
reachability, or really used all the A records they got back, it
might suffice as part of transition to use the EID plus aggregatable
A information. (It's too bad DNS A records do not have preferences
like MX records, but we can't change that now.)
Yours,
Joel
--
to unsubscribe send a message to rrg-request@psg.com with the
word 'unsubscribe' in a single line as the message text body.
archive: <http://psg.com/lists/rrg/> & ftp://psg.com/pub/lists/rrg