you're correct that they calculate sizes differently. Cisco uses the payload size including headers; Juniper just the data-payload size, so for example a 9000 byte layer3 packet for Cisco = 9000 - 20B IP header - 8B ICMP header=8972B for Juniper. you can get them to send unfragmented ICMP packets by turning on the no-fragment flag. On JunOS, it's 'do-not-fragment'; in IOS, it depends a lot on the version but it's there. HTH. brent sweeny, indiana university
On 12/17/2013 8:03 PM, snort bsd wrote: > hi, all: > > i have a genetic question regarding ip fragmentation. i have two routers; one > is cisco and another is juniper. they connected back to back with default > ethernet mtu (cisco 1522 and juniper 1518, of course with vlan on both ends). > i understand that two vendors have different ways of calculating the overhead > of headers. > > > when i send icmp pings, without specifying packets sizes (just default > values) or specifying packet sizes smaller than the values (1472 on juniper > side and 1500 on cisco side), everything is fine, but anything beyond thsoe > two values on both ends, i got nothing. > > i thought that, for ip mtu, anything bigger than ip mtu (or juniper term > protocol mtu) would be fragmented into multiple packets. > > did i miss something or my understanding isn't correct? > > thanks! _______________________________________________ juniper-nsp mailing list juniper-nsp@puck.nether.net https://puck.nether.net/mailman/listinfo/juniper-nsp
