Default routes - Order of preference

From: Nigel Taylor (nigel_taylor@xxxxxxxxxxx)
Date: Wed Feb 14 2001 - 21:36:29 GMT-3

   
<html><DIV>
<P>Hi All,</P>
<P>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; I'm working through as lab
scanerio and I trying to understand; in what order does equal cost default rout
es(0.0.0.0/0) get added to the routing table.&nbsp; How is one default route ma
de the primary over the other.&nbsp; "sh ip ospf data " and "sh ip ospf data ex
t" shows me the following.&nbsp; Looking at the database it would seem that the
 advertising router with the hightest address wins.&nbsp; This being the case i
s there a defined selection process?</P>
<P><BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
&nbsp;&nbsp;&nbsp; Type-5 AS External Link States</P>
<P>Link ID&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; ADV Router&nbsp;&nbs
p;&nbsp;&nbsp;&nbsp; Age&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Seq#&n
bsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Checksum Tag<BR>0.0.0.0&nbsp;&nbsp;&nbsp;&nb
sp;&nbsp;&nbsp;&nbsp;&nbsp; 172.16.255.130 1138&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&n
bsp;&nbsp; 0x80000BD6 0x5049&nbsp;&nbsp; 4<BR>0.0.0.0&nbsp;&nbsp;&nbsp;&nbsp;&n
bsp;&nbsp;&nbsp;&nbsp; 172.116.200.1&nbsp;&nbsp; 721&nbsp;&nbsp;&nbsp;&nbsp;&nb
sp;&nbsp;&nbsp;&nbsp; 0x800007FD 0x79B1&nbsp;&nbsp; 4</P>
<P><BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; OSPF Router with ID (138.139.255.97
) (Process ID 3475)</P>
<P><BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
&nbsp;&nbsp;&nbsp; Type-5 AS External Link States</P>
<P>&nbsp; Routing Bit Set on this LSA<BR>&nbsp; LS age: 1256<BR>&nbsp; Options:
 (No TOS-capability, DC)<BR>&nbsp; LS Type: AS External Link<BR>&nbsp; Link Sta
te ID: 0.0.0.0 (External Network Number )<BR>&nbsp; Advertising Router: 172.16.
255.130<BR>&nbsp; LS Seq Number: 80000BD6<BR>&nbsp; Checksum: 0x5049<BR>&nbsp;
Length: 36<BR>&nbsp; Network Mask: /0<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&n
bsp; Metric Type: 2 (Larger than any link state path)<BR>&nbsp;&nbsp;&nbsp;&nbs
p;&nbsp;&nbsp;&nbsp; TOS: 0 <BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Metr
ic: 1 <BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Forward Address: 0.0.0.0<B
R>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; External Route Tag: 4</P>
<P>&nbsp; Routing Bit Set on this LSA<BR>&nbsp; LS age: 838<BR>&nbsp; Options:
(No TOS-capability, DC)<BR>&nbsp; LS Type: AS External Link<BR>&nbsp; Link Stat
e ID: 0.0.0.0 (External Network Number )<BR>&nbsp; Advertising Router: 172.18.2
00.1<BR>&nbsp; LS Seq Number: 800007FD<BR>&nbsp; Checksum: 0x79B1<BR>&nbsp; Len
gth: 36<BR>&nbsp; Network Mask: /0<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp
; Metric Type: 2 (Larger than any link state path)<BR>&nbsp;&nbsp;&nbsp;&nbsp;&
nbsp;&nbsp;&nbsp; TOS: 0 <BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Metric:
 1 <BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Forward Address: 0.0.0.0<BR>&
nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; External Route Tag: 4</P>
<P>TIA<BR>Nigel</P>
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