I. Statement of problem
Customer desires to have an IRX-112 at site#1 (which we'll call irx1 in
these examples) connect to an IRX-112 or -114 at site#2 (irx2) through
a Frame Relay cloud using port S1, but if that connection is
interrupted dial site#1 automatically using an ISDN TA on port S2. LMI
is used to determine when the link is down. (In ComOS 3.2R you'll be
able to use Annex-D instead of LMI if desired.)
Addresses:
site#1 ether0 204.176.168.241
frm1 204.176.169.66
site#2
ether0 198.246.144.194
frm1 204.176.169.1
II. Explanation of Solution
The way to set this up is to tell irx1 (the remote IRX at site #1) that
its default gateway is the ethernet address of irx2 but with a high
metric, like 4. We'll also tell irx1 to listen for default routes via
its Frame Relay interface. When one of the following three conditions
are met irx1 will no longer have a default route via the Frame Relay
interface, and will fall back to the default route with the higher
metric, causing it to dial out to irx2 via ISDN whenever there is
traffic for offsite. When the Frame Relay interface returns, the
default route will be seen again and packets will be routed via that;
the ISDN line will time out for lack of traffic and hang up.
The critical point to understand in making this possible is that
the IRX doesn't listen to dynamic routes when it has a static route,
EXCEPT for the default route. If it sees a default route that has a
better metric than its static default route, it will accept that but
"push down" the static default route so that its hidden but available
for future use should the dynamic default route disappear.
The three conditions that can trigger dialout are:
1) If your CSU/DSU supports DCD, set it to drop DCD when the
line goes away, and "set s1 modem on" on the IRX. When the CSU/DSU
drops DCD the IRX will reset the s1 port, bringing the Frame Relay
interface down until DCD is asserted again by the CSU/DSU.
When the interface is brought down the routes through it are marked
invalid and the IRX will restore to the backup route.
2) If 6 LMI status packets in a row are missed, the Frame Relay
interface will be brought down until 6 LMI status packets in a row are
received. The usual interval for LMI is 10 seconds, but this can be
adjusted if the TelCo is willing. The TelCo and the setting on the IRX
*must* agree on the LMI interval. (In 3.0R you can use LMI, in 3.2R
you can use either Annex-D or LMI.)
3) If no RIP packets are seen via the Frame Relay interface for 3 minutes
the routes will expire, and the static default route via the ISDN
dialout will become active, triggering a dialout as soon as there is
traffic for offsite.
Similar approaches can be used for leased lines instead of Frame Relay,
and async modems instead of ISDN (using S0).
III. Implementation
Note that synchronous ports on the IRX (s1-s4) ALWAYS require external
clock, so the TelCo or CSU or TA must provide clock to the IRX's serial
port. S1 (or S3) is capable of T1/E1 speeds, S2 (or S4) up to 64k.
On irx1 you would enter the following commands
set sysname irx1
set ether0 address 204.176.168.241
set ether0 broadcast high (or low, depending on preference)
set default listen
set s1 extended on
set s1 protocol frame
set s1 address 204.176.169.66
set s1 lmi 10
set s1 routing on
set s1 modem off (IF your CSU/DSU can assert carrier, "modem on"
would be very useful in this setup)
(Get the Frame Relay interface working before setting up the backup ISDN
link, otherwise the backup will activate!)
set s2 extend on
set s2 network dialout
set s2 protocol ppp
set s2 modem on
set s2 group 2
add netuser irx2
set user irx2 protocol ppp
set user irx2 password what4ever
add location irx2
set location irx2 on_demand
set location irx2 address 198.246.144.194
set location irx2 netmask 255.255.255.0
set location irx2 routing on
set location irx2 protocol ppp
set location irx2 mtu 1500 # adjust to taste
set location irx2 idletime 5 # drop connection after 5 minutes idle
set location irx2 maxports 1
set location irx2 high_water 0
set location irx2 group 2
# replaced 700...4 with phone# for irx2
set location irx2 v25bis 1 "CRN7005551234" "=DCD="
set gateway 198.246.144.194 4 # 4 or HIGHER
save all
reset s1
reset s2
On irx2 (at site#2) you would enter the following commands:
set sysname irx2
set ether0 address 198.246.144.194
set ether0 broadcast high (or low, depending on preference)
set default broadcast
set gateway <ip address of next hop to internet or upstream>
set s1 extended on
set s1 protocol frame
set s1 address 204.176.169.1
set s1 lmi 10
set s1 routing on
set s1 modem off
set s2 extend on
set s2 network dialin
set s2 protocol ppp
set s2 modem on
set s2 idle 5
add netuser irx1
set user irx1 protocol ppp
set user irx1 password what4ever
save all
reset s1
reset s2
-MZ
-- Livingston Enterprises - Chair, Department of Interstitial Affairs Phone: 800-458-9966 510-426-0770 FAX: 510-426-8951 megazone@livingston.com For support requests: support@livingston.com <http://www.livingston.com/> Snail mail: 6920 Koll Center Parkway #220, Pleasanton, CA 94566