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Network Management And Debugging. WeeSan Lee <[email protected]> http://www.cs.ucr.edu/~weesan/cs183/. Roadmap. Interface Configuration Route Configuration Network Debugging. Network Topology. The Internet. 192.168.0.0/24. .2. Router VM. Host VM. .1. .2. 10.0.0.0/24. We will need:

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Network management and debugging

Network Management And Debugging

WeeSan Lee <[email protected]>

http://www.cs.ucr.edu/~weesan/cs183/


Roadmap
Roadmap

  • Interface Configuration

  • Route Configuration

  • Network Debugging


Network topology
Network Topology

The Internet

192.168.0.0/24

.2

Router VM

Host VM

.1

.2

10.0.0.0/24


Interface configuration host vm

We will need:

IP Address

10.0.0.2

Netmask

255.255.255.0

Broadcast

10.0.0.255

Gateway

10.0.0.1

Usually

10.0.0.0 - network

10.0.0.255 - broadcast

Interface Configuration (Host VM)


Interface configuration router vm
Interface Configuration (Router VM)

  • Use ifconfig command

    • $ ifconfig eth1 10.0.0.1 netmask 255.255.255.0

    • $ ifconfig eth1

    • eth1 Link encap:Ethernet HWaddr 00:C0:F0:3C:43:82

    • inet addr:10.0.0.1 Bcast:10.0.0.255 Mask:255.255.255.0

    • UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1

    • RX packets:659988 errors:1 dropped:0 overruns:0 frame:0

    • TX packets:1016790 errors:0 dropped:0 overruns:0 carrier:0

    • collisions:0 txqueuelen:1000

    • RX bytes:73459942 (70.0 Mb) TX bytes:1201693614 (1146.0 Mb)

    • Interrupt:10 Base address:0xd880

  • To bring the interface eth1 down or up via ifconfig command

    • $ ifconfig eth1 down

    • $ ifconfig eth1 up


Interface configuration router vm1
Interface Configuration (Router VM)

  • Edit /etc/sysconfig/network-scripts/ifcfg-eth1

    • DEVICE=eth1

    • ONBOOT=yes

    • #BOOTPROTO=dhcp

    • IPADDR=10.0.0.1

    • NETMASK=255.255.255.0

    • BROADCAST=10.0.0.255

  • To bring up the interface eth1 via ifup script

    • $ ifup eth1

  • To bring down the interface eth1 via ifdown script

    • $ ifdown eth1


Ip aliasing
IP Aliasing

  • A way to assign multiple IP addresses on the same interface

    • $ ifconfig eth1:0 10.0.0.3 netmask 255.255.255.0

    • $ ifconfig eth1:1 10.0.0.4 netmask 255.255.255.0

  • Why?

    • We could experiment new services w/out new HW

    • We could replace problematic HW with IP aliasing on a healthy machine temporary


Route configuration router vm
Route Configuration (Router VM)

  • Default routes

  • Usually added by route command

    • $ route add default gw 192.168.0.1

  • To remove a default route

    • $ route del default gw 192.168.0.1

  • To make it persistent, edit /etc/sysconfig/network

    • NETWORKING=yes

    • HOSTNAME=host1

    • DOMAINNAME=weesan.com

    • GATEWAY=192.168.0.1


Route configuration router vm1
Route Configuration (Router VM)

  • $ netstat -rn

  • Kernel IP routing table

  • Destination Gateway Genmask Flags MSS Window irtt Iface

  • 192.168.0.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0

  • 169.254.0.0 0.0.0.0 255.255.0.0 U 0 0 0 eth0

  • 0.0.0.0 192.168.0.1 0.0.0.0 UG 0 0 0 eth0


Route configuration router vm2
Route Configuration (Router VM)

  • Static routes

  • Usually added by ifconfig command

    • $ route add -net 10.0.0.0 netmask 255.255.255.0 eth1

    • $ route del -net 10.0.0.0 netmask 255.255.255.0 eth1

  • Edit /etc/sysconfig/static-routes

    • eth1 net 10.0.0.0 netmask 255.255.255.0


Route configuration router vm3
Route Configuration (Router VM)

  • $ netstat -rn

  • Kernel IP routing table

  • Destination Gateway Genmask Flags MSS Window irtt Iface

  • 10.0.0.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1

  • 192.168.0.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0

  • 169.254.0.0 0.0.0.0 255.255.0.0 U 0 0 0 eth0

  • 0.0.0.0 192.168.0.1 0.0.0.0 UG 0 0 0 eth0


Enable ip forwarding router vm
Enable IP Forwarding (Router VM)

  • $ echo "1" > /proc/sys/net/ipv4/ip_forward

  • To make it persistent, edit /etc/sysctl.conf

    • Change net.ipv4.ip_forward to 1


Network debugging
Network Debugging

  • Can be tricky

  • Start from one component and work your way through

  • Recommend procedures (bottom-up)

    • Always check power first 

    • Check the LED on the devices

    • Check connectivity, use tools like ping, traceroute, tcpdump, etc

    • Verify application protocol, use telnet


ping

  • Send ICMP-REQUEST and expect ICMP-REPLY

  • $ ping 10.0.0.1

  • PING 10.0.0.1 (10.0.0.1) 56(84) bytes of data.

  • 64 bytes from 10.0.0.1: icmp_seq=1 ttl=64 time=1.18 ms

  • 64 bytes from 10.0.0.1: icmp_seq=2 ttl=64 time=1.57 ms

  • 64 bytes from 10.0.0.1: icmp_seq=3 ttl=64 time=1.03 ms

  • --- 10.0.0.1 ping statistics ---

  • 3 packets transmitted, 3 received, 0% packet loss, time 2002ms

  • rtt min/avg/max/mdev = 1.036/1.263/1.572/0.228 ms


ping

  • Start from known next hop

  • Not always works for remote hosts

    • For example, eon.cs.ucr.edu drops ICMP packets


Traceroute
traceroute

  • Send UDP packets to remote host with TTL 1, 2, 3, …

  • $ [email protected]:~> traceroute www.google.com

  • traceroute: Warning: www.google.com has multiple addresses; using 72.14.253.99

  • traceroute to www.l.google.com (72.14.253.99), 30 hops max, 38 byte packets

  • 1 138.23.211.1 (138.23.211.1) 0.286 ms 0.278 ms 0.353 ms

  • 2 c6513telecom--te-9-4.ucr.edu (138.23.3.105) 25.070 ms 20.486 ms 1.064 ms

  • 3 c6509telecom--te-3-3.ucr.edu (138.23.3.26) 0.384 ms 0.381 ms 0.361 ms

  • 4 riv-dc1.riv-dc1--ucr.cenic.net (137.164.24.121) 0.311 ms 0.235 ms 0.225 ms

  • 5 dc-lax-dc1--riv-dc1-pos.cenic.net (137.164.22.228) 1.457 ms 1.459 ms 1.446 ms

  • 6 * * *

  • 11 po-in-f99.google.com (72.14.253.99) 31.902 ms 30.762 ms 30.745 ms


Tcpdump
tcpdump

  • Originally written by Van Jacobson

  • $ tcpdump

  • $ tcpdump -i eth0

  • $ tcpdump host eon

  • $ tcpdump src net 10.0.0.0/24 and dst port 80

  • $ tcpdump -vvv

  • $ man tcpdump


Reference
Reference

  • LAH

    • Ch 12: TCP/IP Networking

    • Ch 13: Routing

    • Ch 19: Network Management And Debugging


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