I had a cisco 3750 switch that i wanted to enable some vlans for voice on, but only having one DHCP server on a completely seperate vlan to the voice vlans.<\/p>\n\n\n\n
vlan 1 = data (dhcp server on this range)<\/p>\n\n\n\n
vlan 266 = voice (phone dhcp clients on this range)<\/p>\n\n\n\n
PROBLEM<\/strong><\/p>\n\n\n\n The switch for some reason had aload of dhcp server config on it before i started the exercise, so i removed the pools and ran the command: no service dhcp<\/p>\n\n\n\n This was the problem, running this command (no service dhcp) disables dhcp but also disables dhcp relay to, this stops the ip helper-address command from working too.<\/p>\n\n\n\n So even when i put the ip-helper address on the vlan as below it didn’t relay the dhcp broadcasts from the 266 vlan to the dhcp server on vlan 1.<\/p>\n\n\n\n Where 172.19.5.131 is the DHCP server address.<\/p>\n\n\n\n http:\/\/www.cisco.com\/en\/US\/docs\/switches\/lan\/catalyst3550\/software\/release\/12.2_25_seb\/configuration\/guide\/swdhcp82.html#wp1122942<\/a><\/p>\n\n\n\n RESOLUTION<\/strong><\/p>\n\n\n\n So to fix it, i ran the command: <\/p>\n\n\n\n Making sure any dhcp pool configuration has been removed, and this fixed the problem.<\/p>\n","protected":false},"excerpt":{"rendered":" I had a cisco 3750 switch that i wanted to enable some vlans for voice on, but only having one DHCP server on a completely seperate vlan to the voice vlans. vlan 1 = data (dhcp server on this range) vlan 266 = voice (phone dhcp clients on this range) PROBLEM The switch for some … Read more<\/a><\/p>\n","protected":false},"author":4,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[17],"tags":[],"class_list":["post-575","post","type-post","status-publish","format-standard","hentry","category-networking"],"_links":{"self":[{"href":"https:\/\/geekmungus.co.uk\/index.php?rest_route=\/wp\/v2\/posts\/575","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/geekmungus.co.uk\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/geekmungus.co.uk\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/geekmungus.co.uk\/index.php?rest_route=\/wp\/v2\/users\/4"}],"replies":[{"embeddable":true,"href":"https:\/\/geekmungus.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=575"}],"version-history":[{"count":1,"href":"https:\/\/geekmungus.co.uk\/index.php?rest_route=\/wp\/v2\/posts\/575\/revisions"}],"predecessor-version":[{"id":1602,"href":"https:\/\/geekmungus.co.uk\/index.php?rest_route=\/wp\/v2\/posts\/575\/revisions\/1602"}],"wp:attachment":[{"href":"https:\/\/geekmungus.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=575"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/geekmungus.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=575"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/geekmungus.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=575"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}interface Vlan266\n\n description *** VOIP-BBlock ***\n\n ip address 172.29.66.1 255.255.255.0\n\n ip helper-address 172.19.5.131<\/code><\/pre>\n\n\n\nservice dhcp<\/code><\/pre>\n\n\n\n