Information Technology Reference
In-Depth Information
Table18-3
Frame Relay: Cannot ping End to End
Possible Problem
Solution
Split horizon
problem
In a hub-and-spoke Frame Relay environment, you must
configure subinterfaces to avoid problems with split horizon. For
detailed information on configuring subinterfaces, refer to the
Cisco IOS
Wide-Area Networking Configuration Guide
and
Wide-Area Networking Command Reference
.
Frame Relay subinterfaces provide a mechanism for supporting
partially meshed Frame Relay networks. Most protocols assume
transitivity on a logical network; that is, if station A can talk to
station B, and station B can talk to station C, then station A
should be capable of talking to station C directly. Transitivity is
true on LANs, but not on Frame Relay networks, unless A is
directly connected to C.
Additionally, certain protocols such as AppleTalk and
transparent bridging cannot be supported on partially meshed
networks because they require
split horizon
, in which a packet
received on an interface cannot be transmitted out the same
interface even if the packet is received and transmitted on
different virtual circuits.
Configuring Frame Relay subinterfaces ensures that a single
physical interface is treated as multiple virtual interfaces. This
capability enables us to overcome split horizon rules. Packets
received on one virtual interface can now be forwarded out
another virtual interface, even if they are configured on the same
physical interface.
Subinterfaces address the limitations of Frame Relay networks
by providing a way to subdivide a partially meshed Frame Relay
network into a number of smaller, fully meshed (or
point-to-point) subnetworks. Each subnetwork is assigned its
own network number and appears to the protocols as if it is
reachable through a separate interface. (Note that point-to-point
subinterfaces can be unnumbered for use with IP, reducing the
addressing burden that might otherwise result.)
No default
gateway on
workstation
1.
From the local workstation or server, try to
ping
the remote
workstation or server. Make several attempts to
ping
the
remote device if the first
ping
is unsuccessful.
2.
If all your attempts fail, check whether the local workstation
or server can
ping
the local router's Frame Relay interface.
3.
If you are unable to
ping
the local interface, check the local
workstation or server to see whether it is configured with a
default gateway specification.
4.
If no default gateway is specified, configure the device with
a default gateway. The default gateway should be the address
of the local router's LAN interface.
For information on viewing or changing the workstation or
server's default gateway specification, refer to the vendor
documentation.
