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Forum Discussion

GLM_191985's avatar
GLM_191985
Icon for Cirrus rankCirrus
Apr 08, 2019

dns works on 2 ports ?

dns works on 2 ports? port no is same tcp and udp 53 ? why do we need 2 ports. why we using 2 different protocols tcp and udp  
application delivery
LTM
Daniel_Wolf's avatar
Daniel_Wolf
Icon for MVP rankMVP
Apr 08, 2019

DNS will use TCP for Zone Transfer or DNSSEC.

 

DNS will use UDP for answering requests.

 

EDNS (Extension mechanisms for DNS) is a specification for expanding the size of several parameters of the DNS protocol. When using EDNS issues may occur when traversing firewalls , since some firewalls assume a maximum DNS message length of 512 bytes and block longer DNS packets. But still UDP will be used for EDNS.