[j-nsp] auto-negotiation on 1000BASE-X ports

[Martin T]

Nick, Oliver:

by flow control you mean the 'regular' Ethernet flow control using the
PAUSE frame mechanism?


Olivier:

I wasn't aware that remote fault detection is part of the
autonegotiation. Thanks! I tested this out with two directly connected
Juniper M series routers and it works exactly as you described.
However, as I understand, JUNOS allows to enable auto-negotiation
while at the same keep the local interface online despite the fact
that link is unidirectional. I mean the [ auto-negotiation
remote-fault local-interface-online ] and [ auto-negotiation
remote-fault local-interface-offline ] options. For some reason, this
did not work: http://s8.postimg.org/nd5zyo0mr/autoneg_and_remote_fault.png
As you can see, both in case "Remote fault" "Online" or "Offline", the
local interfaces go down if link becomes unidirectional. Any comments
on this behavior?


regards,
Martin

2013/5/6, Olivier Benghozi <olivier.benghozi at wifirst.fr>:
> 1000Base-X can negotiate flow control.
>
> But, an interesting part of autoneg is Remote Fault Notification: one of the
> fibers in your 2 fibers link breaks, and the link becomes unidirectional;
> the side that sees its receiving fiber down sends a frame to notify the
> other side (which didn't see anything special) that the link is down (so
> this side will also show the link as "down", whereas it receives proper
> signal).
> Without this, when a single fiber breaks, to detect (slower) the problem and
> prevent unidirectional GE links, you have to rely on protocols running at a
> higher level: specialized ones (Cisco's UDLD, OAM), on routing protocols, or
> on LACP (which can be used on a single link for this purpose, as would
> describe http://kb.juniper.net/InfoCenter/index?page=content&id=KB13314).
>
> This also exists in 10GE links as Link Fault Signaling.
>
>
> regards,
> Olivier
>
>
>> supported according to IEEE 802.3 22.2.4.4.2)? In a nutshell, why is
>> auto-negotiation needed on 1000BASE-X ports?
>
>