02-19-2008 07:08 AM - edited 03-05-2019 09:14 PM
I have configured many 1602 and 1721 routers and never ran into this problem before. This problem has now happened on two new routers. A 1721 and a 8141 software Ver 12.4 (16).
Using a 56 K wic 1 dsu connected to a frame relay I am able to ping and telnet to the Ip address on the frame side of the router. The frame side address is 10.3.0.44 255.255.255.0! The problem is that I am unable to ping the FastEthernet side of the router without a laptop or other ethernet device connected to the router. The FastEthernet IP address is 10.4.17.1 255.255.255.0! The FastEthernet sh Interfaces cmd shows: the FastEthernet is up but the line protocol is down until something is pluged in. Only then will the line protocol come up and I will then be able to ping the FastEthernet side of the router.
The Sh Run Config is below:
sawmill#
sawmill#sh run
Building configuration...
Current configuration : 1732 bytes
!
! Last configuration change at 13:08:39 EST Fri Feb 15 2008 by sawmill
! NVRAM config last updated at 13:10:49 EST Fri Feb 15 2008 by sawmill
!
version 12.4
no service pad
service timestamps debug datetime
service timestamps log datetime
no service password-encryption
!
hostname sawmill
!
boot-start-marker
boot-end-marker
!
no logging buffered
!
no aaa new-model
!
resource policy
!
clock timezone EST -5
clock summer-time EDT recurring
mmi polling-interval 60
no mmi auto-configure
no mmi pvc
mmi snmp-timeout 180
ip subnet-zero
no ip cef
!
!
no ip dhcp use vrf connected
!
!
no ip domain lookup
!
username sawmill privilege 15 secret xxx
!
!
!
interface FastEthernet0/0
ip address 10.4.17.1 255.255.255.0
ip access-group 101 in
duplex auto
speed auto
!
interface FastEthernet0/1
no ip address
shutdown
duplex auto
speed auto
!
interface Serial0/0/0
bandwidth 56000
ip address 10.3.0.45 255.255.255.0
ip access-group 101 in
ip helper-address 10.3.1.1
ip helper-address 10.3.2.1
encapsulation frame-relay
no fair-queue
frame-relay lmi-type ansi
!
router rip
redistribute connected
network 10.0.0.0
!
ip classless
ip route 10.3.0.0 255.255.255.0 10.3.0.1
ip route 10.3.0.0 255.255.255.0 10.3.0.2
!
no ip http server
!
access-list 101 deny 53 any any
access-list 101 deny 55 any any
access-list 101 deny 77 any any
access-list 101 deny pim any any
access-list 101 permit ip any any
access-list 101 permit icmp any any
snmp-server community ononwep RO
!
control-plane
!
!
line con 0
login local
line aux 0
line vty 0 4
privilege level 15
login local
transport input telnet
line vty 5 15
privilege level 15
login local
transport input telnet
!
sntp server 10.3.1.4
end
sawmill#
Can someone tell me what I'm doing wrong! I have always been able to ping the router on the FastEthernet side before without equipment attached.was there a change in the 12.4(16) software or have I left some thing out of the config file????
Thanks
Jeff
02-19-2008 09:44 AM
Jeff
What you are describing has been standard behavior of IOS for a very long time - if there is not anything plugged in to an Ethernet interface of the router then the Ethernet interface will show as interface is up line protocol is down. The interface comes to up and up when something is plugged in to the interface.
If you want the interface to be up and up even with nothing plugged in then you can add the command no keepalive under the Ethernet interface.
HTH
Rick
02-19-2008 10:30 AM
Thanks Rick
Should this command be removed after an ethernet device is connected for the interface to work properly?
Jeff
02-19-2008 11:09 AM
Jeff
I believe that it would be best to remove the command after some device is connected to the interface.
To put the question into prespective lets think about what the command does and the implications of disabling the interface keepalives. The interface does keepalives as a sort of mechanism to validate whether it is capable of forwarding packets out the interface. If the line protocol is up, then it indicates that keepalives are working and that the interface should be able to forward packets sent to its subnet. If the interface is protocol down then it indicates that it is not able to forward packets sent to its subnet. For Ethernet interfaces when nothing is plugged in then keepalives will fail and the interface will be protocol down.
One implication of interface being protocol down is that you can not ping the interface (which is what you discovered). When you configure the interface to disable keepalives it will go into line protocol up, and it will respond to pings, and it will signal that it can forward packets. So during the period that keepalives are disabled you have created the possibility of a black hole. The router is indicating that it can forward packets out the interface but in fact the packets will drop because there is nothing to forward them to. So enabling keepalives will help the router to accurately report its forwarding status.
HTH
Rick
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