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DHCP snoop Output
In the snoop output, you should see that packets are exchanged between the DHCP client system and the DHCP server system. The IP address for each system is indicated in each packet. IP addresses for any routers or relay agents in the packet's path are also included. If the systems do not exchange packets, the client system might not be able to contact the server system at all. The problem is then at a lower level.
To evaluate snoop output, you must know what the expected behavior is. For example, you must know if the request should be going through a BOOTP relay agent. You must also know the MAC addresses and the IP address of the systems involved so that you can determine if those values are as expected. If there is more than one network interface, you must know the addresses of the network interfaces as well.
The following example shows normal snoop output for a DHCP acknowledgement message sent from the DHCP server on blue-servr2 to a client whose MAC address is 8:0:20:8e:f3:7e. In the message, the server assigns the client the IP address 192.168.252.6 and the host name white-6. The message also includes a number of standard network options and several vendor-specific options for the client.
Example 17-5 Sample snoop Output for One Packet
ETHER: ----- Ether Header ----- ETHER: ETHER: Packet 26 arrived at 14:43:19.14 ETHER: Packet size = 540 bytes ETHER: Destination = 8:0:20:8e:f3:7e, Sun ETHER: Source = 8:0:20:1e:31:c1, Sun ETHER: Ethertype = 0800 (IP) ETHER: IP: ----- IP Header ----- IP: IP: Version = 4 IP: Header length = 20 bytes IP: Type of service = 0x00 IP: xxx. .... = 0 (precedence) IP: ...0 .... = normal delay IP: .... 0... = normal throughput IP: .... .0.. = normal reliability IP: Total length = 526 bytes IP: Identification = 64667 IP: Flags = 0x4 IP: .1.. .... = do not fragment IP: ..0. .... = last fragment IP: Fragment offset = 0 bytes IP: Time to live = 254 seconds/hops IP: Protocol = 17 (UDP) IP: Header checksum = 157a IP: Source address = 10.21.0.4, blue-servr2 IP: Destination address = 192.168.252.6, white-6 IP: No options IP: UDP: ----- UDP Header ----- UDP: UDP: Source port = 67 UDP: Destination port = 68 (BOOTPC) UDP: Length = 506 UDP: Checksum = 5D4C UDP: DHCP: ----- Dynamic Host Configuration Protocol ----- DHCP: DHCP: Hardware address type (htype) = 1 (Ethernet (10Mb)) DHCP: Hardware address length (hlen) = 6 octets DHCP: Relay agent hops = 0 DHCP: Transaction ID = 0x2e210f17 DHCP: Time since boot = 0 seconds DHCP: Flags = 0x0000 DHCP: Client address (ciaddr) = 0.0.0.0 DHCP: Your client address (yiaddr) = 192.168.252.6 DHCP: Next server address (siaddr) = 10.21.0.2 DHCP: Relay agent address (giaddr) = 0.0.0.0 DHCP: Client hardware address (chaddr) = 08:00:20:11:E0:1B DHCP: DHCP: ----- (Options) field options ----- DHCP: DHCP: Message type = DHCPACK DHCP: DHCP Server Identifier = 10.21.0.4 DHCP: Subnet Mask = 255.255.255.0 DHCP: Router at = 192.168.252.1 DHCP: Broadcast Address = 192.168.252.255 DHCP: NISPLUS Domainname = dhcp.test DHCP: IP Address Lease Time = 3600 seconds DHCP: UTC Time Offset = -14400 seconds DHCP: RFC868 Time Servers at = 10.21.0.4 DHCP: DNS Domain Name = sem.example.com DHCP: DNS Servers at = 10.21.0.1 DHCP: Client Hostname = white-6 DHCP: Vendor-specific Options (166 total octets): DHCP: (02) 04 octets 0x8194AE1B (unprintable) DHCP: (03) 08 octets "pacific" DHCP: (10) 04 octets 0x8194AE1B (unprintable) DHCP: (11) 08 octets "pacific" DHCP: (15) 05 octets "xterm" DHCP: (04) 53 octets "/export/s2/base.s2s/latest/Solaris_8/Tools/Boot" DHCP: (12) 32 octets "/export/s2/base.s2s/latest" DHCP: (07) 27 octets "/platform/sun4u/kernel/unix" DHCP: (08) 07 octets "EST5EDT" 0: 0800 208e f37e 0800 201e 31c1 0800 4500 .. .ó~.. .1...E. 16: 020e fc9b 4000 fe11 157a ac15 0004 c0a8 [email protected]...... 32: fc06 0043 0044 01fa 5d4c 0201 0600 2e21 ...C.D..]L.....! 48: 0f17 0000 0000 0000 0000 c0a8 fc06 ac15 ................ 64: 0002 0000 0000 0800 2011 e01b 0000 0000 ........ ....... 80: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 96: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 112: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 128: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 144: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 160: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 176: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 192: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 208: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 224: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 240: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 256: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 272: 0000 0000 0000 6382 5363 3501 0536 04ac ......c.Sc5..6.. 288: 1500 0401 04ff ffff 0003 04c0 a8fc 011c ................ 304: 04c0 a8fc ff40 0964 6863 702e 7465 7374 [email protected] 320: 3304 0000 0e10 0204 ffff c7c0 0404 ac15 3............... 336: 0004 0f10 736e 742e 6561 7374 2e73 756e ....sem.example. 352: 2e63 6f6d 0604 ac15 0001 0c07 7768 6974 com.........whit 368: 652d 362b a602 0481 94ae 1b03 0861 746c e-6+.........pac 384: 616e 7469 630a 0481 94ae 1b0b 0861 746c ific.........pac 400: 616e 7469 630f 0578 7465 726d 0435 2f65 ific...xterm.5/e 416: 7870 6f72 742f 7332 382f 6261 7365 2e73 xport/sx2/bcvf.s 432: 3238 735f 776f 732f 6c61 7465 7374 2f53 2xs_btf/latest/S 448: 6f6c 6172 6973 5f38 2f54 6f6f 6c73 2f42 olaris_x/Tools/B 464: 6f6f 740c 202f 6578 706f 7274 2f73 3238 oot. /export/s2x 480: 2f62 6173 652e 7332 3873 5f77 6f73 2f6c /bcvf.s2xs_btf/l 496: 6174 6573 7407 1b2f 706c 6174 666f 726d atest../platform 512: 2f73 756e 346d 2f6b 6572 6e65 6c2f 756e /sun4u/kernel/un 528: 6978 0807 4553 5435 4544 54ff ix..EST5EDT. |