According to RFC 4890, which four ICMPv6 types are recommended to be allowed to transit a firewall? (Choose four.)
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A. B. C. D. E. F.ABCF.
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RFC 4890 provides recommendations for filtering ICMPv6 traffic in firewalls. ICMPv6 is an important protocol used by IPv6 networks for error reporting, network troubleshooting, and other purposes.
According to RFC 4890, the following ICMPv6 types are recommended to be allowed to transit a firewall:
A. Type 1 - Destination Unreachable: This message is sent by a router or host to inform the sender that the destination is unreachable for some reason (e.g., network unreachable, host unreachable, protocol unreachable). Allowing this type of ICMPv6 message can help with network troubleshooting and can prevent unnecessary retries.
B. Type 2 - Packet Too Big: This message is sent by a router to inform the sender that the packet is too large to be forwarded without fragmentation. Allowing this type of ICMPv6 message can help with Path MTU Discovery (PMTUD), which is important for avoiding fragmentation and reducing packet loss.
C. Type 3 - Time Exceeded: This message is sent by a router to inform the sender that the packet has been discarded because it exceeded the maximum time allowed for its transmission. Allowing this type of ICMPv6 message can help with network troubleshooting and can prevent unnecessary retries.
D. Type 0 - Echo Reply: This message is sent by a host in response to an Echo Request message (Type 8) sent by another host. Allowing this type of ICMPv6 message can be useful for network troubleshooting and monitoring, as well as for verifying connectivity.
It is worth noting that Type 8 - Echo Request is not recommended to be allowed by default, as it can be used for malicious purposes such as ICMP-based attacks.
E. Type 4 - Parameter Problem: This message is sent by a router or host to inform the sender that there is an error in the packet header or options. Allowing this type of ICMPv6 message can help with network troubleshooting and can prevent unnecessary retries.
In summary, according to RFC 4890, the four ICMPv6 types that are recommended to be allowed to transit a firewall are: Destination Unreachable (Type 1), Packet Too Big (Type 2), Time Exceeded (Type 3), and Echo Reply (Type 0).