alternative to router on stick model

[Network Pro]

Hi,

i know you can connect a l2 switch to router via router on stick model. is there any other alternative model to connect this ?

our setup is like this

             layer 3 switch  ---  layer 2 switch --- layer 2 switch

vlan 10     172.21.1.1             172.21.1.2              172.21.1.3          

vlan 20   172.21.2.1             

vlan 30    172.21.3.1              

the above works fine (inter vlan routing through svi)

now third party company has coonneted their router to our switch

             layer 3 switch  ---  layer 2 switch --- layer 2 switch  -------      router (External company) - lan ip address

vlan 10     172.21.1.1             172.21.1.2              172.21.1.3           172.21.1.9   ------  External comapny WAN circuit 

vlan 20   172.21.2.1              

vlan 30   172.21.3.1

172.21.1.9 is the external company fas0/1 address. they have fa0/2 connected to their WAN circuit

now i can access the router from the vlan 10 (172.21.1.1) . in order to access from vlan 20 and vlan 30 i need create sub interface on teh router. thats fine.

but say i add more vlans to my switch, and since this is a router managed by an external company, we cant get them to create sub interface. whats the other way to access their router (our network is on 172.21.x.x range)

someone told me that on the router

int fas0/1

172.21.1.9 255.255..0.0 (/16 subnet instead of /24) will work for all vlans without creating sub interface)  will this ?

OR will this work ?

by adding a default route on the router

ip route 0.0.0.0 0.0.0.0 172.21.1.1 (defaut route poting to our layer 3 switch)

any thoughts  on the above two ways ?

thanks

[p.mcgowan]

you could add static route on external company router

ip route 172.21.2.0 255.255.255.0 172.21.1.1

ip route 172.21.3.0 255.255.255.0 172.21.1.1

if you create 172.21.1.9/16 on inf f0/1 you will have inconsistant mask between your switch and external router.

If you add default route on external router then all their default traffic will come to you, I dont' think you want that!

[Network Pro]

thanks p.mcgowan

jsut wondering if the link between the layer 2 switch (172.21.1.3) and the router 172.21.1.9 is an access port on vlan 10 and not trunk port will it still work as per your ip route  statement ? as that access port will allow only vlan 10 (172.22.1.x) through it, wouldnt it ?