Juniper JN0-636 - Security, Professional (JNCIP-SEC)

According to the security flow trace in the exhibit, the packets are dropped for self but not interested. This means that the SRX device is receiving packets destined to itself, but it does not have the corresponding service configured in the host-inbound-traffic stanza for the interface1. In this case, the service is BGP, which uses TCP port 179. Therefore, the correct action to solve the problem on the SRX device is to add BGP to the allowed host-inbound-traffic for the interface. This can be done by using the following command:

set security zones security-zone interfaces host-inbound-traffic system-services bgp

This command will allow the SRX device to accept BGP packets on the specified interface and zone. Alternatively, the command can be applied to all interfaces in a zone by using the all-interfaces option2.

References: 1: SRX Getting Started - Troubleshoot Security Policy 2: Configuring System Services Allowed for Host Inbound Traffic

The packet is silently discarded because the traceoptions output shows that the packet is dropped with the flag flow_spu_drop, which indicates that the packet is dropped by the SPU without sending any response to the sender. The traceoptions output also shows the reason for the drop as “no session found, start first path. in_tunnel - 0, from_cp_flag - 0” which means that the packet does not match any existing session and is not part of a tunnel or a control plane traffic1.

The packet is part of a new session because the traceoptions output shows that the packet is the first packet of a TCP connection with the flag flow_tcp_syn, which indicates that the packet has the SYN flag set. The traceoptions output also shows that the packet is processed in the first path packet flow with the message “no session found, start first path” which means that the packet is initiating a new session1.

References:

traceoptions (Security Flow) | Junos OS | Juniper Networks

[SRX] How to interpret Flow TraceOptions output for NAT troubleshooting

NAT (Network Address Translation) is a method to map one IP address space into another by modifying network address information in the IP header of packets while they are in transit across a traffic routing device. There are different types of NAT, one of them is the persistent NAT which is a type of NAT that allows you to map the same internal IP address to the same external IP address each time a host initiates a connection.

The exhibit shows the output of the show security macsec statistics interface ge-0/0/70 detail command on an SRX Series device. This command displays the statistics for the Media Access Control Security (MACsec) feature on the ge-0/0/70 interface. MACsec is a feature that provides point-to-point security on Ethernet links by using encryption and data integrity checks. MACsec uses two types of keys to secure the traffic: the Connectivity Association Key (CAK) and the Secure Association Key (SAK). The CAK is used for authentication and key exchange between the MACsec peers. The SAK is used for encryption and decryption of the MACsec traffic.

The two statements that are true based on the exhibit are:

The data that traverses the ge-0/0/70 interface is secured by a secure association key. This is because the exhibit shows that the interface has a Secure Channel (SC) and a Secure Association (SA) established. The SC is a logical connection between the MACsec peers that carries the encrypted traffic. The SA is a subset of the SC that contains the SAK and other parameters for encrypting and decrypting the traffic. The exhibit shows that the interface has encrypted and protected packets, which means that the traffic is secured by the SAK.

The data that traverses the ge-0/0/70 interface cannot be intercepted and read by anyone. This is because the exhibit shows that the interface has encryption enabled. The encryption option indicates whether the MACsec traffic is encrypted or not. If encryption is enabled, the traffic is encrypted by the SAK and cannot be viewed by anyone monitoring the link. If encryption is disabled, the traffic is only protected by the SAK and can be viewed by anyone monitoring the link.

References: Juniper Security, Professional (JNCIP-SEC) Reference Materials source and documents: https://www.juniper.net/documentation/en_US/junos/topics/reference/command-summary/show-security-macsec-statistics-interface-detail.html https://www.juniper.net/documentation/en_US/junos/topics/concept/security-macsec-overview.html