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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
slide14
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
slide15
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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