The route settings are incorrect, causing failure of the ma5100 in-band network management.

Source: Internet
Author: User
Subject: The route settings are incorrect, causing failure of the ma5100 in-band network management.
Code encoding: 0006725
Updated on: 2002.04.24
Author: Zhou Yifan
Reviewer: Hu Hao
Symptom description:
Through the in-band network management of ma5100 through 8750, you cannot ping the IP address with Intranet management of ma5100. It is found that the ping packet remains in the network for a long time and the packet disappears.
Alarm information:
Ping XXX. XXX (ma5100 in-band network management IP address)
TTL expired in transit
TTL expired in transit
TTL expired in transit
Cause analysis:
In TCP/IP networks, the network layer does not guarantee reliable transmission of data packets, but only provides feedback mechanisms (for example, Error Control) through ICMP packets ). The Ping Command is the ICMP request/response packet, and is also the most common test method for the network. The Ping Command is usually used to test interoperability with the following types of message feedback:
1. Request time out
2. Destination Unreachable
3. TTL expired in transit
Scenario 1: when the source machine is pinged to a sink, the source machine cannot receive ICMP response packets within a period of time (after the source machine sends an ICMP request packet, the timer 0 is started, this will happen. The reason for the above problem is that the route from the source to the sink is normal, but the sink to the source has no available path.
Case 2: this problem occurs when no connection is available from the source machine to the sink machine.
Case 3: When the source machine sends an IP packet (ICMP is directly encapsulated in an IP packet), the TTL (time to live) Time of the packet is added, each time a packet passes through a vro, the router will reduce the TTL time of the packet by 1. If the TTL of the packet is 0 before the ICMP request message arrives at the sink, the gateway discards the message and sends the ICMP timeout message to the source machine. The TTL expired in transit message should be displayed on the source machine. This problem occurs mainly because a route loop occurs inside the network, which causes data packets to fail to reach the sink. You can use tracert to track and determine the fault source (it is best to finish the fault on the host when using this command ).

Note: Some routers do not subtract 1 from the package TTL time, but this is generally the case.
Method: If a host is successfully pinged, you can analyze the route hops of data packets from the response information.
I. e. Replay XXX. XXX: byte = xxx time = xxxms TTL = xxx
Use 256 minus the TTL value in the message to obtain the number of Route hops. If the TTL time is too small, a short routing loop may appear in the network.
This situation is prone to when Static Routing is configured. r1_1 is prone to dynamic routing protocols, but r1_2 and OSPF are not prone to this situation.

Processing Process:
1. Use the tracert command to track the routers passing through the target host, and find that the package loops back and forth between the two routers;
2. Check the route table of the faulty vro and find that one of the 8750 route settings is incorrect. As a result, ICMP request packets oscillate between the two 8750;
3. Delete the problematic route, reconfigure the correct route, and restore to normal.
Suggestions and summary:

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