I had saved this as an interesting case to test when I have a chance: In non-routing mode the router apperas to just go to layer 2, encapsulates if possible and sends it on. So since R2 has a point2point, it just uses it, even though nothing in the config points to it. If you turn up the ethernet interface you will see it try to ARP for the destination IP address on the ethernet interface too.
Now here it does something I don't understand - it ARPs on the serial, and gets a reply from R1 which has the MAC of R1's ethernet interface: # debug from R2: Sep 17 17:24:02.518: IP ARP: sent req src 172.32.1.2 000d.6596.3d40, dst 172.16.10.1 0000.0000.0000 Serial0/1 Sep 17 17:24:02.530: IP ARP: rcvd rep src 172.16.10.1 0011.2027.7f20, dst 172.32.1.2 Serial0/1 # show arp: Internet 192.168.1.1 - 000d.6596.3d40 ARPA FastEthernet0/0 Internet 172.16.10.1 0 0011.2027.7f20 HDLC Serial0/1 ????? If you disable proxy-arp on R1's facing serial interface, while at R2 the ethernet interface is up, it will no longer be able to reach 172.16.10.1. ??? The issue with having a loopback is nothing special BTW. R2 here just uses it as the default source IP address and then R1 doesn't know how to reply back. If you use the serial as the source the ping works fine. Martin On Tue, Sep 1, 2009 at 11:23 AM, <[email protected]>wrote: > Send CCIE_RS mailing list submissions to > [email protected] > > To subscribe or unsubscribe via the World Wide Web, visit > http://onlinestudylist.com/mailman/listinfo/ccie_rs > or, via email, send a message with subject or body 'help' to > [email protected] > > You can reach the person managing the list at > [email protected] > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of CCIE_RS digest..." > > > Today's Topics: > > 1. Re: No IP Routing ISSUE (Taqdir Singh) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Tue, 1 Sep 2009 20:53:24 +0530 > From: Taqdir Singh <[email protected]> > Subject: Re: [OSL | CCIE_RS] No IP Routing ISSUE > To: "Mashburn, Vince" <[email protected]> > Cc: "[email protected]" <[email protected]> > Message-ID: > <[email protected]> > Content-Type: text/plain; charset="iso-8859-1" > > Please find attached configurations + diagram > > Just again my question is > > How I am able to ping 172.16.10.1 from R2 where there is no route + even no > default gateway configured ? > > I am really curious to know. > > > > On Tue, Sep 1, 2009 at 8:46 PM, Mashburn, Vince <[email protected] > >wrote: > > > Send us the configs of you R0 please. > > > > > > > > Thanks, > > > > Vince Mashburn > > > > > > > > > > > > *From:* [email protected] [mailto: > > [email protected]] *On Behalf Of *Taqdir Singh > > *Sent:* Tuesday, September 01, 2009 8:00 AM > > *To:* cyrus riobah > > *Cc:* [email protected] > > *Subject:* Re: [OSL | CCIE_RS] No IP Routing ISSUE > > > > > > > > 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 > > > > > > -- > Taqdir Singh > CCNP- (R), CCNA > 09911709496 > > Do today what others won't so you can live tomorrow as others can't > -------------- next part -------------- > An HTML attachment was scrubbed... > URL: > http://onlinestudylist.com/pipermail/ccie_rs/attachments/20090901/3deea4bd/attachment.htm > -------------- next part -------------- > R0#sh run > Building configuration... > > Current configuration : 790 bytes > ! > version 12.4 > service timestamps debug datetime msec > service timestamps log datetime msec > no service password-encryption > ! > hostname R0 > ! > boot-start-marker > boot-end-marker > ! > ! > no aaa new-model > memory-size iomem 5 > ! > ! > ip cef > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > interface Loopback0 > ip address 172.16.10.1 255.255.255.0 > ! > interface Serial0/0 > ip address 10.1.1.1 255.255.255.0 > serial restart-delay 0 > ! > interface Serial0/1 > no ip address > shutdown > serial restart-delay 0 > ! > interface Serial0/2 > no ip address > shutdown > serial restart-delay 0 > ! > interface Serial0/3 > no ip address > shutdown > serial restart-delay 0 > ! > ip http server > no ip http secure-server > ip route 0.0.0.0 0.0.0.0 Serial0/0 > ! > ! > ! > ! > ! > ! > control-plane > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > line con 0 > line aux 0 > line vty 0 4 > ! > ! > end > > R0# > -------------- next part -------------- > R1#sh run > Building configuration... > > Current configuration : 752 bytes > ! > version 12.4 > service timestamps debug datetime msec > service timestamps log datetime msec > no service password-encryption > ! > hostname R1 > ! > boot-start-marker > boot-end-marker > ! > ! > no aaa new-model > memory-size iomem 5 > ! > ! > ip cef > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > interface Serial0/0 > no ip address > shutdown > serial restart-delay 0 > ! > interface Serial0/1 > ip address 10.1.1.2 255.255.255.0 > serial restart-delay 0 > ! > interface Serial0/2 > ip address 172.32.1.1 255.255.255.0 > serial restart-delay 0 > ! > interface Serial0/3 > no ip address > shutdown > serial restart-delay 0 > ! > ip http server > no ip http secure-server > ip route 172.16.10.0 255.255.255.0 Serial0/1 > ! > ! > ! > ! > ! > ! > control-plane > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > line con 0 > line aux 0 > line vty 0 4 > ! > ! > end > > R1# > -------------- next part -------------- > R2#sh run > Building configuration... > > Current configuration : 803 bytes > ! > version 12.4 > service timestamps debug datetime msec > service timestamps log datetime msec > no service password-encryption > ! > hostname R2 > ! > boot-start-marker > boot-end-marker > ! > ! > no aaa new-model > memory-size iomem 5 > no ip routing > ! > ! > no ip cef > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > interface Serial0/0 > no ip address > no ip route-cache > shutdown > serial restart-delay 0 > ! > interface Serial0/1 > no ip address > no ip route-cache > shutdown > serial restart-delay 0 > ! > interface Serial0/2 > ip address 172.18.10.1 255.255.255.0 > no ip route-cache > serial restart-delay 0 > ! > interface Serial0/3 > ip address 172.32.1.2 255.255.255.0 > no ip route-cache > serial restart-delay 0 > ! > ip http server > no ip http secure-server > ! > ! > ! > ! > ! > ! > control-plane > ! > ! > ! > ! > ! > ! > ! > ! > ! > ! > line con 0 > line aux 0 > line vty 0 4 > ! > ! > end > > R2# > -------------- next part -------------- > A non-text attachment was scrubbed... > Name: routing problem.jpg > Type: image/jpeg > Size: 11183 bytes > Desc: not available > Url : > http://onlinestudylist.com/pipermail/ccie_rs/attachments/20090901/3deea4bd/attachment.jpg > > End of CCIE_RS Digest, Vol 44, Issue 9 > ************************************** >
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