On 3/31/15 1:10 PM, Rabadan, Jorge (Jorge) wrote:
Hi Robert and Tony,
As Wim mentioned, ipv6 anycast is something that we will add to the
draft in the next rev. There is an easy way to know if a given
proxy-ND entry belongs to an anycast address or not and disable the
duplicate IP detection for those.
The challenge for IPv4 is that I don’t see an easy way to learn
_dynamically_ from access attachment circuits that a given ipv4 is
anycast. Even for default gateways, if they are integrated in the EVPN
PE, we are good, but if they are external and connected to a MAC-VRF,
it is not so clear how to learn that (unless you learn those entries
from the management interface).
Jorge,
IPv4/ARP doesn't have any support for anycast address on the same
subnet. While IPv6/ND has such support (using the O-flag) the common
anycast deployment for both is to have the anycast instances deployed on
different subnets and, in the case of DNS servers, in different ISPs.
Thus for IPv4 I think you can assume that the same IP address appearing
with different MAC addresses is either a duplicate IP address or a case
of a host having changed the MAC address on its NIC. (I don't know if
NIC bonding can be configured in a way where it looks like an IP->MAC
change each time there is a failure; if so that would be a third case.)
Erik
One of the reasons why we have lots of “SHOULDs” in the draft and not
“MUST” is because the implementation has to be flexible enough to be
configured in a different way depending on the use-case, which is one
of the points that Tony mentions below. In the use-case described at
the moment there is no anycast and duplicate IP detection is very
important. We will add the DC use case in the next rev as suggested by
Robert and others.
Thanks.
Jorge
From: Antoni Przygienda <[email protected]
<mailto:[email protected]>>
Date: Monday, March 30, 2015 at 12:12 AM
To: Robert Raszuk <[email protected] <mailto:[email protected]>>,
"Henderickx, Wim (Wim)" <[email protected]
<mailto:[email protected]>>
Cc: Erik Nordmark <[email protected] <mailto:[email protected]>>,
"[email protected] <mailto:[email protected]>" <[email protected]
<mailto:[email protected]>>, Jorge Rabadan
<[email protected]
<mailto:[email protected]>>
Subject: RE: [bess] ARP ND draft
I’m also skeptical whether IP duplicate detection would be a good
default thing. Especially in case of what I call ‘aliased default
gateway’ which section 10.1 specifically allows, i.e. default GW
IP address is same but each PE may use a different MAC when
advertising it and consequently responses for same IP with
different ARPs may be seen in the network. Yes, default GW
ExtComm is there to differentiate so it can be called an exception
but nevertheless.
I also thought a tad about VRRP but I think the IP duplicate
detection will not apply there, it’s all same IPx->MACx from all
routers so if anything, it’s more of a MAC move thing.
Generally I think someone who wants a secure, stable eVPN wants IP
duplicate detection, someone who runs a very dynamic network with
tons gateways, possibly anycast & floating IPs will probably not
be too enamored with it.
Thanks
--- tony
//
/There are basically two types of people. People who accomplish
things, and people who claim to have accomplished things. The
first group is less crowded.
<http://www.brainyquote.com/quotes/quotes/m/marktwain393535.html>/
/~~~ Mark Twain
<http://www.brainyquote.com/quotes/quotes/m/marktwain393535.html>/
*From:*[email protected] <mailto:[email protected]>
[mailto:[email protected]] *On Behalf Of *Robert Raszuk
*Sent:* Monday, March 30, 2015 1:19 AM
*To:* Henderickx, Wim (Wim)
*Cc:* Erik Nordmark; Antoni Przygienda; [email protected]
<mailto:[email protected]>; Rabadan, Jorge (Jorge)
*Subject:* Re: [bess] ARP ND draft
Hi Wim,
> There is anycast at IPv4 level for sure but I am not ware this is
supported at arp level.
Precisely right. It needs to be documented and addressed if anyone
is up to proposing automated IP duplicate address detection and
disabling.
RFC1546 is rather too old to consider here as solution :)
Cheers,
R.
On Mon, Mar 30, 2015 at 1:10 AM, Henderickx, Wim (Wim)
<[email protected]
<mailto:[email protected]>> wrote:
To be clear: RFC4861 section 7.2.7 explains the anycast behaviour
in IPv6.
I am not aware of such thing at IPv4/ARP level. Do you have a pointer?
There is anycast at IPv4 level for sure but I am not ware this is
supported at arp level.
*From: *<Henderickx>, Wim Henderickx
*Date: *Monday 30 March 2015 07:38
*To: *Robert Raszuk
*Cc: *Erik Nordmark, Antoni Przygienda, "[email protected]
<mailto:[email protected]>", Jorge Rabadan
*Subject: *Re: [bess] ARP ND draft
At interface level you get dad in most stacks I know.
Sent from my iPhone
On 30 Mar 2015, at 06:45, Robert Raszuk <[email protected]
<mailto:[email protected]>> wrote:
Hi Wim,
What makes you say that in IPv4 there is no anycast ? All
anycase I have played so far is IPv4 :)
Cheers,
r.
On Sun, Mar 29, 2015 at 11:18 PM, Henderickx, Wim (Wim)
<[email protected]
<mailto:[email protected]>> wrote:
We will update the draft to highlight the IPv6 anycast
behaviour better as pointed out by RObert. In IPv4 there is no
anycast behaviour and as such there should be one option possible.
On 30/03/15 04:59, "Antoni Przygienda"
<[email protected]
<mailto:[email protected]>> wrote:
>Yes, but of course I brought it up to show that 'the last one
simply wins' as suggested by the draft is not enough IMO. A
good architecture should probably keep track of what it served
as answer and when the answer is invalid or a new, better one
exists, provide a GARP.
>
>As well, when PE2 sends a newer MAC it may not be a good
strategy to serve a GARP if PE1's MAC has already been
offered. That could lead IMO to e.g. gateway chasing problems.
>
>--- tony
>
>
>There are basically two types of people. People who
accomplish things, and people who claim to have accomplished
things. The first group is less crowded.
>~~~ Mark Twain
>
>
>> -----Original Message-----
>> From: Henderickx, Wim (Wim)
[mailto:[email protected]
<mailto:[email protected]>]
>> Sent: Thursday, March 26, 2015 6:01 AM
>> To: Antoni Przygienda; Erik Nordmark; Rabadan, Jorge (Jorge)
>> Cc: [email protected] <mailto:[email protected]>
>> Subject: Re: [bess] ARP ND draft
>>
>> For this case you should sent a GARP with the new MAC/IP
>>
>>
>>
>>
>> On 25/03/15 18:56, "Antoni Przygienda"
<[email protected]
<mailto:[email protected]>>
>> wrote:
>>
>> >> > b)It is worth explaining what is suggested behavior if
eVPN
>> >> > advertises the same IP with multiple MACs and what
happens when
>> >> > e.g. the served MAC vanishes
>> >> >
>> >> Doesn't the EVPN RFC already stating that the routes
would be
>> >> withdrawn in that case?
>> >
>> >The scenario I had in mind was when eVPN PE receives
>> >
>> >From PE2 IP1/M1 and later
>> >From PE3 IP1/M2
>> >
>> >while having answered with IP1/M1 per proxy alrady.
Additionally, in
>> >such situation ends up seeing
>> >
>> >From PE2 IP1/<no MAC>
>> >
>> >So the answer it gave is not valid anymore all of a sudden.
>> >
>> >--- tony
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