TCP IP Illustrated

Interface mtu recall our experiment in section 116 in

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Unformatted text preview: ort.140.252.1.29.1023.140.252.1.11.513=513 For the rlogin to gemini only one entry appears, since gemini is a different host. We only see the client end of the connection (local port 1023), but both ends of the Telnet connection appear (client port 1415 and server port 23), since the connection is through the loopback interface. We can also see that the listening FTP server has a local IP address of 0.0.0.0, indicating it will accept connections on any interface. 25.9 Additional Examples We now return to some earlier problems we encountered in the text, and use SNMP to understand what's happening. Interface MTU Recall our experiment in Section 11.6, in which we tried to determine the MTU of the SLIP link from netb to sun. We can now use SNMP to obtain this MTU. We first obtain the interface number (ipRoutelfIndex) of the SLIP link (140.252.1.29) from the IP routing table. Using this we go into the interface table and fetch the MTU (along with the description and type) of the SLIP link: sun % snmpi -a netb -c secret snmpi> get ipRouteIfIndex.140.252.1.29 ipRouteIfIndex.140.252.1.29=12 snmpi> get ifDescr.l2 ifType.12 ifMtu.l2 ifDescr.l2="Telebit NetBlazer dynamic dial virtual interface" ifType.l2=other(1) file:///D|/Documents%20and%20Settings/bigini/Doc...omenet2run/tcpip/tcp-ip-illustrated/snmp_sim.htm (26 of 33) [12/09/2001 14.47.40] Chapter 25. SNMP: Simple Network Management Protocol ifMtu.l2=1500 We see that even though the link is a SLIP link, the MTU is set to the Ethernet value of 1500, probably to avoid fragmentation. Routing Tables Recall our discussion of address sorting performed by the DNS in Section 14.4. We showed how the first IP address returned by the name server was the one that shared a subnet with the client. We also mentioned that using the other IP address would probably work, but could be less efficient. Let's look at using the alternative IP address and see what happens. We'll use SNMP to look at a routing table entry, and tie together many concepts from earlier chapters dealing with IP routing. The host g...
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This test prep was uploaded on 04/04/2014 for the course ECE EL5373 taught by Professor Guoyang during the Spring '12 term at NYU Poly.

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