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Network Management And Debugging

Network Management And Debugging. WeeSan Lee <weesan@cs.ucr.edu> 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

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  1. Network Management And Debugging WeeSan Lee <weesan@cs.ucr.edu> http://www.cs.ucr.edu/~weesan/cs183/

  2. Roadmap • Interface Configuration • Route Configuration • Network Debugging

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

  4. 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)

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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

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

  16. traceroute • Send UDP packets to remote host with TTL 1, 2, 3, … • $ weesan@delta-1:~> 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

  17. 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

  18. Reference • LAH • Ch 12: TCP/IP Networking • Ch 13: Routing • Ch 19: Network Management And Debugging

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