You have three routers in your topology. Your successful ping happens the following way.
R2 send to r1 with a source of 172.32.1.2 and dest of 172.16.10.1 R1 receives the packet and uses the static route to forward it to R0 R1# ip route 172.16.10.0 255.255.255.0 Serial0/1 R0 receives the packet on S0/0. R0 now does a lookup for the source to send the echo reply, the echo reply is sent using the default route to s0/1 on R1. r0# ip route 0.0.0.0 0.0.0.0 Serial0/0 R1 does a lookup for the destination and since it's locally attached it is forwarded on to s0/3 of R2 When you add a loopback to R2, R2 uses the loopback interface as the source of the ping and is unable to forward it to R1. If you add the loopback to R2 then source the ping from the serial interface it should work. Let me know if this makes sense. Thanks, Justin On Tue, Sep 1, 2009 at 12:16 PM, Joe Astorino <[email protected]>wrote: > hmmmmm.... debug ip packet see whats going on there. I've seen some > strange things similar to this on serial links before. > > > On Tue, Sep 1, 2009 at 11:28 AM, Taqdir Singh <[email protected]>wrote: > >> *R2#ping 172.16.10.1* >> >> Type escape sequence to abort. >> Sending 5, 100-byte ICMP Echos to 172.16.10.1, timeout is 2 seconds: >> !!!!! >> Success rate is 100 percent (5/5), round-trip min/avg/max = 8/56/132 ms >> *R2#sh ip route* >> Default gateway is not set >> >> Host Gateway Last Use Total Uses Interface >> ICMP redirect cache is empty >> *R2#sh ip int brief* >> Interface IP-Address OK? Method >> Status Protocol >> Serial0/0 unassigned YES unset administratively >> down down >> Serial0/1 unassigned YES unset administratively >> down down >> Serial0/2 unassigned YES manual administratively >> down down >> Serial0/3 172.32.1.2 YES manual >> up up >> R2# >> >> >> >> On Tue, Sep 1, 2009 at 7:59 PM, Bryan Bartik <[email protected]>wrote: >> >>> Taqdir >>> >>> Give us a "sho ip int brief" on R2... >>> >>> On Tue, Sep 1, 2009 at 7:00 AM, Taqdir Singh >>> <[email protected]>wrote: >>> >>>> Please note , I am sitting on* router R2* and I am pinging from there >>>> to loopback 172.16.10.1 which on router R0. >>>> >>>> *On router R2 - I have disabled ip routing*. then how come I am able to >>>> ping loopback on router R0* even if there is no route in R2*? >>>> >>>> On Tue, Sep 1, 2009 at 6:15 PM, cyrus riobah <[email protected]>wrote: >>>> >>>>> Its never possible to be able to ping over a serial link (in fact a >>>>> network on different subnets) without the routing involved. >>>>> >>>>> With the output of sh ip route on your R0, the statement ""S* >>>>> 0.0.0.0/0 is directly connected, Serial0/0"" indicates that this is s >>>>> static route readily configured to R0 hence makes it to ping anything >>>>> connected to R0. >>>>> >>>>> Possibly, check all your router for a static route, S* indicates its >>>>> existence. >>>>> >>>>> Regards >>>>> >>>>> Cyrus >>>>> >>>>> CCNP,CCDA,ARFE,WAAS,AWLANFE,XF >>>>> >>>>> On 9/1/09, Taqdir Singh <[email protected]> wrote: >>>>> > Please see my attached diagram. >>>>> > Just curious to know , how ping is successfull sitting on router R2 >>>>> to >>>>> > destination 172.16.10.1 though on R2 I have disabled ip routing and >>>>> even >>>>> > there is no default-gateway configured. >>>>> > >>>>> > Other curious thing I want to know - If i configure any loopback >>>>> interface >>>>> > on router R2.. and then try to ping 172.16.10.1 it is unsuccessfull. >>>>> > >>>>> > Could any1 please help whats going on here on router R2 ? >>>>> > >>>>> > R0#sh ip ro >>>>> > Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP >>>>> > D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area >>>>> > N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 >>>>> > E1 - OSPF external type 1, E2 - OSPF external type 2 >>>>> > i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS >>>>> level-2 >>>>> > ia - IS-IS inter area, * - candidate default, U - per-user >>>>> static >>>>> > route >>>>> > o - ODR, P - periodic downloaded static route >>>>> > >>>>> > Gateway of last resort is 0.0.0.0 to network 0.0.0.0 >>>>> > >>>>> > 172.16.0.0/24 is subnetted, 1 subnets >>>>> > C 172.16.10.0 is directly connected, Loopback0 >>>>> > 10.0.0.0/24 is subnetted, 1 subnets >>>>> > C 10.1.1.0 is directly connected, Serial0/0 >>>>> > S* 0.0.0.0/0 is directly connected, Serial0/0 >>>>> > R0#echo reply rcvd, src 172.16.10.1, dst 172.32. >>>>> > R0# >>>>> > ================ >>>>> > >>>>> > R1#sh ip ro >>>>> > Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP >>>>> > D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area >>>>> > N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 >>>>> > E1 - OSPF external type 1, E2 - OSPF external type 2 >>>>> > i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS >>>>> level-2 >>>>> > ia - IS-IS inter area, * - candidate default, U - per-user >>>>> static >>>>> > route >>>>> > o - ODR, P - periodic downloaded static route >>>>> > >>>>> > Gateway of last resort is not set >>>>> > >>>>> > 172.16.0.0/24 is subnetted, 1 subnets >>>>> > S 172.16.10.0 is directly connected, Serial0/1 >>>>> > 172.32.0.0/24 is subnetted, 1 subnets >>>>> > C 172.32.1.0 is directly connected, Serial0/2 >>>>> > 10.0.0.0/24 is subnetted, 1 subnets >>>>> > C 10.1.1.0 is directly connected, Serial0/1 >>>>> > R1# >>>>> > ===================== >>>>> > >>>>> > R2#sh ip ro >>>>> > Default gateway is not set >>>>> > >>>>> > Host Gateway Last Use Total Uses >>>>> Interface >>>>> > ICMP redirect cache is empty >>>>> > R2#ping 172.16.10.1 >>>>> > >>>>> > Type escape sequence to abort. >>>>> > Sending 5, 100-byte ICMP Echos to 172.16.10.1, timeout is 2 seconds: >>>>> > !!!!! >>>>> > Success rate is 100 percent (5/5), round-trip min/avg/max = 12/48/136 >>>>> ms >>>>> > R2# >>>>> > >>>>> > >>>>> > -- >>>>> > Taqdir Singh >>>>> > CCNP- (R), CCNA >>>>> > 09911709496 >>>>> > >>>>> > Do today what others won't so you can live tomorrow as others can't >>>>> > >>>>> >>>> >>>> >>>> >>>> -- >>>> Taqdir Singh >>>> CCNP- (R), CCNA >>>> 09911709496 >>>> >>>> Do today what others won't so you can live tomorrow as others can't >>>> >>>> _______________________________________________ >>>> For more information regarding industry leading CCIE Lab training, >>>> please visit www.ipexpert.com >>>> >>>> >>> >>> >>> -- >>> Bryan Bartik >>> CCIE #23707 (R&S), CCNP >>> Sr. Support Engineer - IPexpert, Inc. >>> URL: http://www.IPexpert.com <http://www.ipexpert.com/> >>> >> >> >> >> -- >> Taqdir Singh >> CCNP- (R), CCNA >> 09911709496 >> >> Do today what others won't so you can live tomorrow as others can't >> >> _______________________________________________ >> For more information regarding industry leading CCIE Lab training, please >> visit www.ipexpert.com >> >> > > > -- > Regards, > > Joe Astorino - CCIE #24347 R&S > Technical Instructor - IPexpert, Inc. > Cell: +1.586.212.6107 > Fax: +1.810.454.0130 > Mailto: [email protected] > > _______________________________________________ > For more information regarding industry leading CCIE Lab training, please > visit www.ipexpert.com > >
_______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com
