LANCOM Support Knowledgebase Document No. 0906.0908.4137.LFRA - V1.50

Traces – IP router trace explained



Traces - general:

LANCOM routers provide the option of logging internal processes in order to diagnose errors. This trace function can be accessed from the telnet console or by means of the trace module in LANmonitor. Below you will find a IP router trace with the meaning of each message explained.


Application:

The purpose of the IP router trace is to check how the router processes TCP/IP packets which arrive at it.
You can check whether the packets were received and where they are forwarded to.
You can also recognize packets that have been filtered or rejected.

To do this, enter the command "trace + ip-router" at a telnet console.
    Important:
    In LCOS 10.20 changes have been made regarding the IP-Router trace. These are described in the following article in our knowledgebase: Dokumentlinksymbol


IP-router trace in detail:

A client connected via VPN sends a ping to an IP address in the local network INTRANET:

[IP-Router] 2008/02/20 11:01:35,970Timestamp, prefixed to every packet
IP-Router Rx (BUGFIX, RtgTag: 0):The IP router has received a packet (Rx) from the remote station BUGFIX. This packet has the routing tag (RtgTag) "0"
DstIP: 10.98.0.65, SrcIP: 10.100.7.1, Len: 84, DSCP/TOS: 0x00The destination address (DstIP) and the source address (SrcIP) are shown.
Also shown is the packet length (Len), in this case 84 bytes, and also the DiffServ/Type of Service field (DSCP/TOS), in the case empty: 0x00
Prot.: ICMP (1), echo request, id: 0x66d0, seq: 0x0000The protocol (Prot), in this case ICMP, the ID and the sequence number are displayed
Route: LAN Tx (INTRANET):The packet is transmitted to the LAN interface and then to the LAN network INTRANET
[IP-Router] 2008/02/20 11:01:35,970
IP-Router Rx (LAN-1, INTRANET, RtgTag: 0):
DstIP: 10.100.7.1, SrcIP: 10.98.0.65, Len: 84, DSCP/TOS: 0x00
Prot.: ICMP (1), echo reply, id: 0x66d0, seq: 0x0000
Route: WAN Tx (BUGFIX)
An answer packet from the Intranet is forwarded to the WAN remote station.

Another data packet (this time the POP3 protocol):


[IP-Router] 2008/02/20 11:19:510.530Timestamp, prefixed to every packet
IP-Router Rx (WLAN-1, INTRANET, RtgTag: 0):The IP router has received a packet (Rx) from the physical interface WLAN-1 of the logical network INTRANET. This packet has the routing tag (RtgTag) "0"
DstIP: 129.216.119.235, SrcIP: 10.98.0.67, Len: 46, DSCP/TOS: 0x00The destination address (DstIP) and the source address (SrcIP) are shown.
Also shown is the packet length (Len), in this case 46 bytes, and also the DiffServ/Type of Service field (DSCP/TOS), in the case empty: 0x00
Prot.: TCP (6), DstPort: 110, SrcPort: 4889, Flags: PADisplayed here are the protocol (Prot), in this case TCP, the destination port (DstPort), in this case 110, the source port (SrcPort), in this case 4889, and the TCP flag of the packet
Route: WAN Tx (INTERNET)The packet is transmitted to the WAN interface, the remote station INTERNET
[IP-Router] 2008/02/20 11:19:51,550
IP-Router Rx (INTERNET, RtgTag: 0):
DstIP: 10.98.0.67, SrcIP: 129.216.119.235, Len: 208, DSCP/TOS: 0x00
Prot.: TCP (6), DstPort: 4889, SrcPort: 110, Flags: PA
Route: WLAN-1 Tx (INTRANET):
The answer packet from the Internet is forwarded to the local WLAN.

Frequent error messages and their meaning in the IP-router trace:

Error message: No route => discard frame:

[IP-Router] 2008/02/20 11:43:32,440
IP-Router Rx (intern, RtgTag: 0):
DstIP: 192.168.200.1, SrcIP: 10.98.0.70, Len: 84, DSCP/TOS: 0x00
Prot.: ICMP (1), echo request, id: 0x2533, seq: 0x0000
no route => discard frame
The destination network cannot be reached because there is no routing entry for this network in the routing table.
The packet is dropped.


Meaning:
The destination network cannot be reached. For this reason the packet is dropped.

Possible causes:
- There is no route to the network. Create a route to the destination network, or check the destination address


Error message: Filter (route)

[IP-Router] 2008/02/20 11:22:30,770
IP-Router Rx (WLAN-1, INTRANET, RtgTag: 0):
DstIP: 192.168.1.1, SrcIP: 10.98.0.67, Len: 30, DSCP/TOS: 0x00
Prot.: UDP (17), DstPort: 5060, SrcPort: 5060
Filter (Route)
The packets are filtered, because the address range is private and the routing table blocks these.

Meaning:
The route to the destination network is blocked. For this reason the packet is filtered.

Possible causes:
- The route to the destination network is blocked. Check the destination address, create a dedicated route for the destination, or unblock the route if the destination network can be reached via the default route.



Catchwords:
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