diff --git a/Test_Cases/Test_Case1/readme b/Test_Cases/Test_Case1/readme
index d54d931..704f8fe 100644
--- a/Test_Cases/Test_Case1/readme
+++ b/Test_Cases/Test_Case1/readme
@@ -27,3 +27,7 @@ For the FIN+ACK packet, the FIN and ACK flags in the header have a value of 1.
 18. TCP Checksum = initially zero, then:
 (i) Concatenate TCP Pseudo header (Protocol, Source IP, Destination IP, Total Length) with TCP header and TCP data. This creates a big integer.
 (ii) Convert this integer to binary and compute bit wise 1's complement. 
+
+References:
+1. https://www.thegeekstuff.com/2012/05/ip-header-checksum/
+2. https://www.tutorialspoint.com/calculation-of-tcp-checksum
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