Differences

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--- networking:ping [2021/11/15 07:53] – created bstafford
+++ networking:ping [2022/11/23 12:49] (current) – external edit 127.0.0.1
@@ Line 2: / Line 2: @@
 ===== Ping without Framenting =====
+Data from Palo Alto Networks [[https://knowledgebase.paloaltonetworks.com/KCSArticleDetail?id=kA10g000000PN0gCAG|here]].
 -f will mean that the ping is only sent if it isn't fragmented.
 -l sets the size of the packet
-<code>ping -f 10.1.1.1 -l 1400</code>
+<code>ping -f 10.1.1.1 -l 1472</code>
+The reason to chose 1472 Bytes as the size for the first test is because the complete packet will then be 1500 Bytes.
+Complete Packet = 20B(IP Header) + 8B(ICMP Header) + 1472B(Payload) = 1500 Bytes.
+Divide and conquer method has been used to find the Max value where the ping succeeds.
+Based on the above test outputs it can be seen that the ping works when size is 1372 Bytes and fails when it is 1373 Bytes.
+This means only a 1400 Bytes packet will be able to reach the server and back without getting fragmented.
+Bytes + ICMP header 8 Bytes + IP header 20 Bytes = 1400 Bytes.
+To determine the Optimal MSS that can be used, take the result of the above test which is 1400 Bytes and subtract the potential TCP header and IP header value.
+Bytes - (IP header 20 Bytes + TCP header 20 Bytes) = 1360 Bytes.
+So the Optimal MSS that can be used is 1360 Bytes.
+On PA firewall to adjust the MSS value to 1360 Bytes, the Adjustment size has to be configured as 140 Bytes.
+- 1360 = 140 Bytes
+===== Windows Show MTU =====
+Show MTU on Windows. It is in the left column
+<code>netsh interface ipv4 show subinterface</code>