More Fragments

Fragment Headers Verify

Each fragment header has its own recomputed IP header checksum.

highlighted = computed this step

Each header gets its own checksum

The first fragment checksum is 0xd1fe; the second fragment checksum is 0xf204.

0xd1fe,0xf2040xd1fe,0xf204
Both headers verifyEach fragment header has its own recomputed IPv4 header checksum.Fragment 1 verify - verifyrowindexvalueword00x4500word10x0024word20x1c46word30x2000word40x4006word50xd1feword60xac10word70x0a63word80xac10word90x0a0craw sum0x0002fffdfolded0xffffresult0xffffFragment 2 verify - verifyrowindexvalueword00x4500word10x001cword20x1c46word30x0002word40x4006word50xf204word60xac10word70x0a63word80xac10word90x0a0craw sum0x0002fffdfolded0xffffresult0xffff

First fragment verifies

Including checksum 0xd1fe, the first fragment folds to 0xffff.

first fold=0xffff\text{first fold}=0xffff
Both headers verifyEach fragment header has its own recomputed IPv4 header checksum.Fragment 1 verify - verifyrowindexvalueword00x4500word10x0024word20x1c46word30x2000word40x4006word50xd1feword60xac10word70x0a63word80xac10word90x0a0craw sum0x0002fffdfolded0xffffresult0xffffFragment 2 verify - verifyrowindexvalueword00x4500word10x001cword20x1c46word30x0002word40x4006word50xf204word60xac10word70x0a63word80xac10word90x0a0craw sum0x0002fffdfolded0xffffresult0xffff

Second fragment verifies

Including checksum 0xf204, the second fragment also folds to 0xffff.

second fold=0xffff\text{second fold}=0xffff
Both headers verifyEach fragment header has its own recomputed IPv4 header checksum.Fragment 1 verify - verifyrowindexvalueword00x4500word10x0024word20x1c46word30x2000word40x4006word50xd1feword60xac10word70x0a63word80xac10word90x0a0craw sum0x0002fffdfolded0xffffresult0xffffFragment 2 verify - verifyrowindexvalueword00x4500word10x001cword20x1c46word30x0002word40x4006word50xf204word60xac10word70x0a63word80xac10word90x0a0craw sum0x0002fffdfolded0xffffresult0xffff

Summary

Different fragment header fields mean different recomputed IP version 4 header checksums.

valid fold=0xffff\text{valid fold}=0xffff
Both headers verifyEach fragment header has its own recomputed IPv4 header checksum.Fragment 1 verify - verifyrowindexvalueword00x4500word10x0024word20x1c46word30x2000word40x4006word50xd1feword60xac10word70x0a63word80xac10word90x0a0craw sum0x0002fffdfolded0xffffresult0xffffFragment 2 verify - verifyrowindexvalueword00x4500word10x001cword20x1c46word30x0002word40x4006word50xf204word60xac10word70x0a63word80xac10word90x0a0craw sum0x0002fffdfolded0xffffresult0xffff