From: Ellis, Neil (Neil.Ellis@xxxxxxxxxxxx)
Date: Fri Jan 11 2002 - 15:50:12 GMT-3
LUU:
It depends on the routing protocol in use. OSPF uses a hello and dead
interval. The hello depending upon the network type is default at 10
seconds. The dead interval is always 4 times the hello interval. If a
neighbor is not heard from by the time the dead interval is expired it is
assumed down and taken out of the neighbor table. The hello interval can be
manually manipulate with the interface command ip ospf hello-interval.
http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121cgcr/ip_r
/iprprt2/1rdospf.htm#xtocid796920
At the time that the dead interval expires that router is no longer a
neighbor and that whole routing table is taken out. The SPF tree also has to
be recalculated. Good resources are Jeff Doyle TCP/IP Volume I and a new
Cisco press book CCIE Practical Studies. Must reads for anyone attempting
the CCIE Lab!
With Eigrp neighbors are communicated with in a similar manner. Hellos are
multicast out every 5 seconds or 60 seconds depending on the network type.
It can be manipulated with the interface command ip hello-interval eigrp.
http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121cgcr/ip_r
/iprprt2/1rdeigrp.htm#xtocid1895711
The hello will include a hold time which is three times the hello timer.
This determines how long to wait for another hello from the sending
neighbor. Once that timer has expired the neighbor is considered gone. The
default for hold time can be manipulated with the interface command ip
hold-time eigrp.
http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121cgcr/ip_r
/iprprt2/1rdeigrp.htm#xtocid1895712
As with OSPF once the neighbor adjacency is lost all routes from that
neighbor is cleared from the routing table.
RIP has an expiration timer or timeout for routes in the routing table.
Cisco may refer to it as an invalid timer. This is set at a default of 180
seconds or 6 update periods. The protocol will change a route's hop count to
16 or unreachable if it has not been given an update for that particular
route. Updates in the Cisco world can vary (according to Jeff Doyle's TCP/IP
Volume I) between 25.5 to 30 seconds. Now there's another timer called the
flush timer that is set to 240 seconds. The route is advertised as
unreachable until that timer expires. At that time the route is finally
removed from the router. The last timer is referred to as the holddown
timer. Is is used when an update is received with a hop count greater than
what exists in the current routing table. The protocol will place this route
into holddown for 180 seconds.
I hope all of this helps it is available in TCP/IP Volume I by Jeff Doyle.
Good luck to all!
Best Regards,
Neil Ellis MCSE, CCNP,CCDP,A+,Net+,i-Net+,
Network Engineer
Converged Solutions
* Neil.Ellis@expanets.com
* 303-300-6320 x6224
Cell 303-548-9453
-----Original Message-----
From: Huy Luu [mailto:Huy_Luu%COMMONWEALTH@ccginc.com]
Sent: Friday, January 11, 2002 11:08 AM
To: ccielab@groupstudy.com
Subject: EIGRP routes
When Eigrp, OSPF, RIP or any routing protocol looses a neighbor and does
not have alternative route to networks advertised by the down neighbor,
how long does it take for that neighbor's routes to dissapear from the
routing table? Is there a default timeout value for routes in the
routing table?Any link from CCO will be greatly appreciated. Thanks all
for your help.
This archive was generated by hypermail 2.1.4 : Thu Jun 13 2002 - 10:56:25 GMT-3