Strange speed problems with ipv6 forwarding

[Frank Steiner]

Andras Toth wrote

> Hi Frank,
> 
> As Matt and me earlier pointed out it sounds like the router is
> sending ICMP Redirects because they are on a common segment and the
> router tries to tell the host a better route exist. You can read more
> about redirects here:
> http://www.cisco.com/c/en/us/support/docs/ip/routing-information-protocol-rip/13714-43.html

Well, it does sound reasonable and like my configuration is bad
because it prevents the better route. I can fix this for the static
hosts, but we also allow laptops with dhcp in this segment, and
they get their information from a dhcp server that is not in my
control, and the same...


> The slowness occurs as the router cannot forward packets in its
> dedicated fast circuits (ASIC or data-plane) because it needs to send
> an ICMP Redirect packet to each packet on the same subnet. This is
> done in the router CPU (control-plane) which is slower than the
> dedicated circuits in the router data-plane.
> 
> Try disabling IPv6 redirects, on Cisco routers it's generally "no ipv6
> redirects" on the routed interfaces, such as the L3 ports or VLAN
> Interfaces (SVI). Alternatively fix your topology and routing to
> ensure the return traffic does not go through the router in the same
> subnet.

...holds for the router, it's managed by our data center. I will write
them a mail about this issue and ask for a change in the config, but
I don't know if they will care about nit :-)

Anyway, your explanations helped to understand what's going on and
as I can easily fix this for my own hosts that suffered from this
problem, you both helped me a lot, thank you very much!

If our data center is willing to change the configuration, I'll
let you know if it helped!

cu,
Frank

-- 
Dipl.-Inform. Frank Steiner   Web:  http://www.bio.ifi.lmu.de/~steiner/
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