Question : How ICMP packet on R2 knows that it has to come out from serial with IP 172.32.1.2 to reach 172.16.10.1 ?
On Wed, Sep 2, 2009 at 6:42 AM, Taqdir Singh <[email protected]> wrote: > > Question : How ICMP packet on R2 knows that it has to come out from serial > with IP 172.32.1.2 to reach 172.16.10.1 ? > > > > > On Tue, Sep 1, 2009 at 11:35 PM, Justin Guagliata <[email protected]>wrote: > >> 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 >>> >>> >> > > > -- > 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
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