how to use static ADSL as backup connection

July sall · ‎05-04-2011

hi all,

i need some design help on the situation here.

we have a few WAN connecting sites to ISP using BGP. we are looking at getting backup link for 1 site.

we have decide to use an IPWAN ADSL link. we will have 877 and 2800 for each link.

from understanding, we have a static routing on IPWAN service. means when both BGPWAN and IPWAN connected to the ISP. ISP will use ADSL as primary ignore the BGP link. so other sites will see a BGP route coming from ISP via the ADSL link for this location.

so we have find a manuel solution, leave ADSL unpluged of power but setup same lan ip address and connect the cable towards the core swich. when WAN link fail, swith on ADSL. So the static route will advertise to the rest of sites.

just want to know is there any auto solution can disable the ADSLlink/ppp link when the 2800/WAN route is up. and enable the ADSL port when the WAN is down. not sure if HSRP/backup interface/tracking will work? and how?

site office swith - > 2800 - > ISP

- > ADSL -> ISP (need this link to be backup and protocol down, so the ISP will not able to connect to this link and advertise as nexthop)

thanks

jon

Thotsaphon Lueangwattanaphong · ‎05-05-2011

Hi,

HSRP can help you solve this problem. R2800 and R877 can run HSRP on their LAN interface and then the switch can point the default gateway to the virtual IP address that can be configured. You just give a hight priority for R2800 and do interface tracking on it. If wan interface's R2800 is down,the switch will send packets to R877. In case Wan inteface's R2800 come back up,the switch will get back to use R2800 again.

Ref : http://www.cisco.com/en/US/tech/tk648/tk362/technologies_tech_note09186a0080094e8c.shtml

Are you running BGP on R877 as well? If so,we might have to do more.

HTH,

Toshi

July sall · ‎05-05-2011

hi there

no, 877 is running as a static default route towards ISP. once the ADSL is up, the ISP will redistribute the ADSL link to all other sites via BGP. therefore the WAN BGP will not be used.

we are looking for a way to keep the 877 router running with ADSL port shutdown. Once the 2800 WAN link fails/ our BGP will fail, the ADSL/ppp link enable itself. so all traffic will go via ADSL. (the problem is if 877, 2800 WAN link both up, ISP will perfer 877 adsl link)

is it possible? HSRP will solve the local issue where 877, 2800 LAN port can have a vitual interface. however it doesn't solve the issue where 877 ADSL WAN port is up once the router power up.

any ideas?

thanks in advance.

Thotsaphon Lueangwattanaphong · ‎05-05-2011

Hi Jon,

Like I mentioned, HSRP will help you control the switch to route to the correct router we defined. In this case seems you have to control the routing on BGP as well. Does R2800 advertise internal networks to BGP? Please explain a bit more about how you advertise routes in BGP.

If you want to go what you mentioned. You have to add a WIC-Adsl card on your R2800 and then use "Backup interface" functions. This will let ADSL ack as a standby link. However,R2800 is a sigle point of failure.

R2800: 2 Wan interfaces

+

interface s0/0/0

backup interface dialer 0

+

HTH,

Toshi

July sall · ‎05-05-2011

hi toshi,

you are 100% right, HSRP will control the local office. our 2800 router use BGP to advertise internal routes to other sites. however the ADSL static route is done by the ISP. once the ADSL link is up the local site internal address(we provide to the ISP on this ADSL setup) will be advertised to all other sites with a higher prority.

therefore we can't have both ADSL and WAN running in the same time.

as you mentioned, new ADSL card in 2800 with backup command might solve this issue. but as you said its a single point of fail which is reason why we get the backup link in the first place.

mmm..seems running out of options. is there any command i can use such as object tracking can achieve this?

because the technolgy on the link is decided and ordered. otherwise maybe an adsl internet link with VPN is better option, as least we have full control of the routing. another thing, i think we tried VPN before, the latency is about 2-4 times higher then the IPWAN solution.

thanks

Jon

Thotsaphon Lueangwattanaphong · ‎05-05-2011

Hi Jon,

Are you using the same ISP for 2 links?

once the ADSL link is up the local site internal address(we provide to the ISP on this ADSL setup) will be advertised to all other sites with a higher prority.

Can we change this behavior? It doesn't make any sense to give backup link hight priority.

HTH,

Toshi