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New Member

problems with ospf and secondary addr - subinterfaces on eth


i have the following problem:

we want to connect our ibm-host over a fiber-gigabit-ethernet to our cisco 65xx router/switch.

on the host we have 4 different lpars.

we have to use ospf between the 4 lpars and the router - so we decided to make 4 different transit-net

between host and router.

we made this with ip-secondary-adrress - then we saw that ospf does NOT send Hellos on secondary addr.

so this was no solution.

the second thing was to implement 802.1q and subinterfaces - but our host does not understand 802.1q

Is it possible to configure subinterfaces on a gigabit-eth-link without trunking ????

If no - why (if it would be frame-relay, it would be possible - so why not in eth ??)

The last idea is to make only one L3 Subnet and to place all lpars and the router in this one subnet !

Can anyone answer my questions ??


  • Other Network Infrastructure Subjects
New Member

Re: problems with ospf and secondary addr - subinterfaces on eth


the question is: "why do you need 4 IP addresses on the host and 4 routing peers between

the router and the host?" The OSPF process should announce all configured networks, so

there is no need for more than one routing peer.

regards Ulrich Marzoli

Cisco Employee

Re: problems with ospf and secondary addr - subinterfaces on eth

you can't make sub-interfaces on ehternet unless you enable trunking.

The reason is simple. Trunking adds another encapsulation so that you can differentiate a packet sent in sub-interface 1 from sub-interface 2.

Frame Relay uses the same principle with different DLCI assigned to each sub-interface.

So, the question is why do you need 4 ospf sessions over 1 single physical interface ?

Normally, 1 session should be enough to advertise all 4 addresses.

If you really need it, could add more hardware to your host and have 4 physical interfaces ?

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