"encapsulation failed" incomplete ARP

[Ray_Bcomplex]

I'm attempting to use my 2514 router between my DSL modem and my Linksys wireless router. I'm running 12.2(8)T and PPPoE is on the modem. Eth0 is set to 'ip address dhcp' and correctly obtains the public IP from the modem.
I can resolve DNS such as 'google.com' and it returns the correct IP address. However, I cannot get a ping to go through. After running debugs, i find that the ping is reporting "encapsulation failed".
More debugging shows the IP address in my ARP table reports 'Incomplete' for google's entry. If i statically put the modems MAC address in with the corresponding IP address(such as for google) i can sucessfully PING google.com

what can i do to have the router automatically resolve all arp requests to the modem? it's probably something very simple that i'm overlooking, but very annoying! if i hook up my computer directly to the modem, it has no issues. any advice?

[Big Evil]

This means that the router knows on which interface it has to send the packet, but does not know how to do it.
Try to create a sticky mac on the router?

[HermeszData]

I'm attempting to use my 2514 router between my DSL modem and my Linksys wireless router. I'm running 12.2(8)T and PPPoE is on the modem. Eth0 is set to 'ip address dhcp' and correctly obtains the public IP from the modem.
I can resolve DNS such as 'google.com' and it returns the correct IP address. However, I cannot get a ping to go through. After running debugs, i find that the ping is reporting "encapsulation failed".
More debugging shows the IP address in my ARP table reports 'Incomplete' for google's entry. If i statically put the modems MAC address in with the corresponding IP address(such as for google) i can sucessfully PING google.com

what can i do to have the router automatically resolve all arp requests to the modem? it's probably something very simple that i'm overlooking, but very annoying! if i hook up my computer directly to the modem, it has no issues. any advice?

Can you post the config for the interface in question?

[Ray_Bcomplex]

Can you post the config for the interface in question?


Hoover#sho ver
Cisco Internetwork Operating System Software
IOS (tm) 2500 Software (C2500-IS-L), Version 12.2(8)T, RELEASE SOFTWARE (fc2)
TAC Support: http://www.cisco.com/tac
Copyright (c) 1986-2002 by cisco Systems, Inc.
Compiled Wed 13-Feb-02 21:11 by ccai
Image text-base: 0x0306DA78, data-base: 0x00001000

ROM: System Bootstrap, Version 5.2(8a), RELEASE SOFTWARE
BOOTLDR: 3000 Bootstrap Software (IGS-RXBOOT), Version 10.2(8a), RELEASE SOFTWARE (fc1)

Hoover uptime is 2 minutes
System returned to ROM by power-on
System image file is "flash:/c2500.bin"

cisco 2500 (68030) processor (revision D) with 16384K/2048K bytes of memory.
Processor board ID 05268328, with hardware revision 00000000
Bridging software.
X.25 software, Version 3.0.0.
2 Ethernet/IEEE 802.3 interface(s)
2 Serial network interface(s)
32K bytes of non-volatile configuration memory.
16384K bytes of processor board System flash (Read ONLY)
--More--  
Configuration register is 0x2102

Hoover#sho run
Building configuration...

Current configuration : 869 bytes
!
version 12.2
no service pad
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
!
hostname Hoover
!
!
ip subnet-zero
ip cef
!
!
!
!
interface Ethernet0
ip address dhcp
no ip proxy-arp
ip nat outside
no cdp enable
--More--  !
interface Ethernet1
ip address 172.17.1.1 255.255.255.0
no cdp enable
!
interface Serial0
ip address 172.16.14.17 255.255.255.248
ip nat inside
no ip mroute-cache
no cdp enable
!
interface Serial1
no ip address
shutdown
no cdp enable
!
ip default-gateway 192.168.0.1
ip nat inside source list 101 interface Ethernet0 overload
ip classless
ip route 0.0.0.0 0.0.0.0 Ethernet0
ip route 192.168.0.0 255.255.0.0 Ethernet0
no ip http server
no ip pim bidir-enable
--More--  !
!
access-list 101 permit ip any any
no cdp run
!
!
line con 0
line aux 0
line vty 0 4
login
!
end

Hoover#
--------------------------------
192.168.0.1 is my modem

[HermeszData]

ip default-gateway 192.168.0.1
ip nat inside source list 101 interface Ethernet0 overload
ip classless
ip route 0.0.0.0 0.0.0.0 Ethernet0
ip route 192.168.0.0 255.255.0.0 Ethernet0
no ip http server
no ip pim bidir-enable
--More--  !
!
access-list 101 permit ip any any
no cdp run
!
!
line con 0
line aux 0
line vty 0 4
login
!
end

Hoover#
--------------------------------
192.168.0.1 is my modem

First, I would kill the route to E0 referencing 192.168.0.0 - This is a route to a private network and is also redundant to:

ip route 0.0.0.0 0.0.0.0 e0 because this is your outside interface.

second:

what does sh ip int br give as results?

[Ray_Bcomplex]

Hoover#en
Hoover#sh ip int brie
Interface IP-Address OK? Method Status Protocol
Ethernet0 99.xxx.xxx.129 YES DHCP up up
Ethernet1 172.17.1.1 YES NVRAM up down
Serial0 172.16.14.17 YES NVRAM down down
Serial1 unassigned YES NVRAM administratively down down
Hoover#sh arp
Protocol Address Age (min) Hardware Addr Type Interface
Internet 99.191.73.129 - 00e0.b063.b064 ARPA Ethernet0
Internet 74.125.19.103 - 000b.2364.04f0 ARPA
Internet 172.17.1.1 - 00e0.b063.b065 ARPA Ethernet1
Hoover#ping google.com
Translating "google.com"...domain server (192.168.0.1) [OK]

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 74.125.19.147, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
Hoover#ping lammle.com
Translating "lammle.com"...domain server (192.168.0.1) [OK]

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 174.132.212.194, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
Hoover#conf t
Enter configuration commands, one per line. End with CNTL/Z.
Hoover(config)#arp 174.132.212.194 000b.2364.04f0 arpa
Hoover(config)#do ping lammle.com

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 174.132.212.194, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 60/63/64 ms
Hoover(config)#do show arp
Protocol Address Age (min) Hardware Addr Type Interface
Internet 99.191.73.129 - 00e0.b063.b064 ARPA Ethernet0
Internet 174.132.212.194 - 000b.2364.04f0 ARPA
Internet 74.125.19.103 - 000b.2364.04f0 ARPA
Internet 192.168.0.1 2 000b.2364.04f0 ARPA Ethernet0
Internet 172.17.1.1 - 00e0.b063.b065 ARPA Ethernet1
Hoover(config)#do ping yahoo.com
Translating "yahoo.com"...domain server (192.168.0.1) [OK]

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 69.147.114.224, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
Hoover(config)#do sho arp
Protocol Address Age (min) Hardware Addr Type Interface
Internet 99.191.73.129 - 00e0.b063.b064 ARPA Ethernet0
Internet 174.132.212.194 - 000b.2364.04f0 ARPA
Internet 74.125.19.103 - 000b.2364.04f0 ARPA
Internet 69.147.114.224 0 Incomplete ARPA
Internet 192.168.0.1 2 000b.2364.04f0 ARPA Ethernet0
Internet 172.17.1.1 - 00e0.b063.b065 ARPA Ethernet1
Hoover(config)#

[HermeszData]

From your last post, and looking back at your config, I would venture a quess that the problem is with your default-gateway CLI.

In config mode. type in:
no ip default-gateway (May have to include the ip address)

Your default gateway is your modem. the modem's ip address will be on the same network as the ip address of E0:

Internet 99.191.73.129 - 00e0.b063.b064 ARPA Ethernet0

[Ray_Bcomplex]

the IP it's offering the 2514 on e0 is the public address, to address the modem it's 192.168.0.1. i understand the first bolded part of your quote, that's easy, but i don't get the second part..... explain?


From your last post, and looking back at your config, I would venture a quess that the problem is with your default-gateway CLI.

In config mode. type in:
no ip default-gateway (May have to include the ip address)

Your default gateway is your modem. the modem's ip address will be on the same network as the ip address of E0:

[HermeszData]

the IP it's offering the 2514 on e0 is the public address, to address the modem it's 192.168.0.1. i understand the first bolded part of your quote, that's easy, but i don't get the second part..... explain?

Your connection should be:

Router ---> Modem ---> ISP

How did you determine your modem's IP address?

Based on the sh ip int br output, the ip address of the modem CANNOT be 192.168.0.1.

Here is why! The modem becomes, in effect the, DHCP server! The normal way ISPs work is they will assign an address to the modem and unless the modem is also acting as a router, it will in turn assign an ip address within the same subnet to a single device attached to it. In the case the modem is acting as a router, and some do, the modem will assign a private IP address to devices connected to it.the only time this does not happen is if you have purchased a single static IP address and in that case the modem uses a "bridging" technique.

Therefore, IF your router is being assigned a PUBLIC IP address via DHCP, your modem Cannot have an IP address as you state! The ISP effectively tells the modem what its IP address and how to assign DHCP addresses. Routers can only directly communicate with directly connected devices on the same subnet. the IP address of 99.8.8.8 is on a completely different subnet (Class B Public), even a different network class, than 192.168.0.1 (Class C Private)

So, telling the router that the default gateway is 192.168.0.1 when you have NO INTERFACE with an IP address on that subnet, confuses the router and it CANNOT COMMUNICATE because it has nowhere to send packets!

Basic network connectivity 101

[Ray_Bcomplex]

Hoover(config)#do trace google.com

Type escape sequence to abort.
Tracing the route to google.com (74.125.19.103)

1 192.168.0.1 4 msec 8 msec 8 msec
2 adsl-99-191-75-254.dsl.pltn13.sbcglobal.net (99.191.75.254) 16 msec 16 msec
12 msec
3 76.246.22.130 12 msec 16 msec 16 msec
4 69.220.8.95 16 msec 16 msec 16 msec
5 151.164.95.196 20 msec 16 msec 16 msec
6 72.14.198.105 16 msec 16 msec 16 msec
7 216.239.49.250 16 msec 16 msec 16 msec
8 209.85.251.94 28 msec 20 msec 16 msec
9 google.com (74.125.19.103) 16 msec 16 msec 16 msec
----------------------------------------------------------------
Hoover(config)#do ping 192.168.0.1

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.0.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/5/8 ms

i understand the concept behind what you're saying, in terms of basic network 101 stuff. i was unaware that my ISP dictated dhcp terms to my modem though. i was under the impression the modem simply passed on its own assigned address and acted as a transparent conduit. on the modem it has the option to assign out the public address, or make up a private one.

[HermeszData]

Hoover(config)#do trace google.com

Type escape sequence to abort.
Tracing the route to google.com (74.125.19.103)

1 192.168.0.1 4 msec 8 msec 8 msec
2 adsl-99-191-75-254.dsl.pltn13.sbcglobal.net (99.191.75.254) 16 msec 16 msec
12 msec
3 76.246.22.130 12 msec 16 msec 16 msec
4 69.220.8.95 16 msec 16 msec 16 msec
5 151.164.95.196 20 msec 16 msec 16 msec
6 72.14.198.105 16 msec 16 msec 16 msec
7 216.239.49.250 16 msec 16 msec 16 msec
8 209.85.251.94 28 msec 20 msec 16 msec
9 google.com (74.125.19.103) 16 msec 16 msec 16 msec
----------------------------------------------------------------
Hoover(config)#do ping 192.168.0.1

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.0.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/5/8 ms

i understand the concept behind what you're saying, in terms of basic network 101 stuff. i was unaware that my ISP dictated dhcp terms to my modem though. i was under the impression the modem simply passed on its own assigned address and acted as a transparent conduit. on the modem it has the option to assign out the public address, or make up a private one.

... do you have your modem configured regarding DHCP?