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Route Iteration Is Found in a Special Application Scenario

Publication Date:  2012-07-27 Views:  47 Downloads:  0
Issue Description

In a GSM wireless network, the Datacom devices serve as its bearer network. The basic topology is as follows:

CBC (wireless equipment) --Datacom bearer network -- NE40 � GBAM (wireless equipment) -- XPUC (wireless equipment)

Datacom equipment serves as the wireless bearer network. The purpose is to ensure that the CBC can ping the XPUC successfully. As a result, the existing network cannot be pinged. Even the NE40, which serves as a direct connection device between the Datacom equipment and the GBAM, fails to ping the XPUC.
Alarm Information
Null
Handling Process

Though the static route features a lower priority than a direct route, it has a more accurate mask. You may add it to the routing table. Attempt to add similar routes to other routers. The operation fails.

Use the ip route-static 10.1.1.3 32 g1/0/0 10.1.1.2 command to attempt to add the static route. The route is added and delivered to the FIB table. The problem is solved and the network connection is normal.

The analysis indicates that the static route without using an outbound interface involves route iteration. In Huawei, route iteration follows a rule, that is, a dependent route cannot be a supernet route of a destination route. The problem is solved.
Root Cause

The networking at the wireless end is as follows: To the external network, the GBAM has only one IP address, such as 10.1.1.2/24; to the internal network (all wireless equipment), the GBAM has a private IP address. The public address is in the same network segment as the NE40 port (such as GE 1/0/0, 10.1.1.1/24). The XPUC also has only one public IP address, such as 10.1.1.3/32.

The GBAM has only two directions to forward data and it does not support ARP proxy.

Thus, for the NE40, the XPUC is in the same network segment. The XPUC, however, is not directly accessible. The NE40 cannot learn the corresponding ARP. Therefore, the connection fails.

This wireless application seems irrational, but the first possible method is to add a static route on the NE40. Point the route of 10.1.1.3/32 to the next hop 10.1.1.2.

Use the ip route-static 10.1.1.3 32 10.1.1.2 command to add the static route. Run the display ip routing-table protocol static command to view route details. The route is found inactive.
Suggestions

The simplest iteration is the fact that a static route is configured with a next hop but without an outbound interface. This involves multiple iteration rules. Therefore, the best static route should follow a next hop plus an outbound interface.

Of course, in most cases, the rule "a dependent route cannot be a supernet route" should be followed. It prevents data in a broadcasting network from being forwarded according to a non-optimal path. In some cases, however, this rule could be a problem.

END