Network Management And Debugging

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Network Management And Debugging

• WeeSan Lee ltweesan_at_cs.ucr.edugt
• http//www.cs.ucr.edu/weesan/cs183/

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Roadmap

• Interface Configuration
• Route Configuration
• Network Debugging

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Network Topology
The Internet
192.168.0.0/24
.2
Router VM
Host VM
.1
.2
10.0.0.0/24
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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

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Interface Configuration (Router VM)

• Use ifconfig command
• ifconfig eth1 10.0.0.1 netmask 255.255.255.0
• ifconfig eth1
• eth1 Link encapEthernet HWaddr
  00C0F03C4382
• inet addr10.0.0.1 Bcast10.0.0.255
  Mask255.255.255.0
• UP BROADCAST RUNNING MULTICAST
  MTU1500 Metric1
• RX packets659988 errors1 dropped0
  overruns0 frame0
• TX packets1016790 errors0 dropped0
  overruns0 carrier0
• collisions0 txqueuelen1000
• RX bytes73459942 (70.0 Mb) TX
  bytes1201693614 (1146.0 Mb)
• Interrupt10 Base address0xd880
• To bring the interface eth1 down or up via
  ifconfig command
• ifconfig eth1 down
• ifconfig eth1 up

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Interface Configuration (Router VM)

• Edit /etc/sysconfig/network-scripts/ifcfg-eth1
• DEVICEeth1
• ONBOOTyes
• BOOTPROTOdhcp
• IPADDR10.0.0.1
• NETMASK255.255.255.0
• BROADCAST10.0.0.255
• To bring up the interface eth1 via ifup script
• ifup eth1
• To bring down the interface eth1 via ifdown
  script
• ifdown eth1

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IP Aliasing

• A way to assign multiple IP addresses on the same
  interface
• ifconfig eth10 10.0.0.3 netmask 255.255.255.0
• ifconfig eth11 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

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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
  
• NETWORKINGyes
• HOSTNAMEhost1
• DOMAINNAMEweesan.com
• GATEWAY192.168.0.1

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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

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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

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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

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Enable IP Forwarding (Router VM)

• echo "1" gt /proc/sys/net/ipv4/ip_forward
• To make it persistent, edit /etc/sysctl.conf
• Change net.ipv4.ip_forward to 1

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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

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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_seq1 ttl64
  time1.18 ms
• 64 bytes from 10.0.0.1 icmp_seq2 ttl64
  time1.57 ms
• 64 bytes from 10.0.0.1 icmp_seq3 ttl64
  time1.03 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

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ping

• Start from known next hop
• Not always works for remote hosts
• For example, eon.cs.ucr.edu drops ICMP packets

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traceroute

• Send UDP packets to remote host with TTL 1, 2, 3,
  
• weesan_at_delta-1gt 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

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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

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Reference

• LAH
• Ch 12 TCP/IP Networking
• Ch 13 Routing
• Ch 19 Network Management And Debugging