SRX

Q. When is dual data‐links supported for HA and how do they function on the high-end SRX?

a. For SRX 3000 and 5000 series, Starting in JUNOS 10.2 we support dual data links. There is no additional hardware required forthis feature, so long has you have two physical links per chassis to support the dual data links

When dual data‐links are both functional, the first data link will be utilized only for the RTO synchronization and Probes, while the second link will be used for sending the inter‐chassis user traffic in the case of Active / Active mode (where traffic is arriving on an interface on node 0 and leaves an egress interface on node 1, or vice versa). If either link fails (but one remains up) then all RTO’s, Probes, and in the case of Active/Active, all user traffic will be failed over to the other link.

To give more information on both control link and data links for high-end SRX:

a. SRX 3k:
i. Starting in JUNOS 10.2, we support dual control links, however each SRX in the cluster must have 1 true RE in the RE0 slot, and the SRX3K‐CRM in RE1 module of each chassis. This means that you will need 2 RE’s, and 2 SRX3K‐CRM’s total, one of each for each chassis.
ii. Starting in JUNOS 10.2 we support dual data links. There is no additional hardware required for this feature, so long has you have two physical links per chassis to support the dual data links.
b. SRX 5k
i. Starting in JUNOS 10.0, if you have dual RE’s in each chassis (total of 4 RE’s, two for each chassis) then we do support the ability to configure dual control links. Unlike the SRX 3k, there is no special CRM required, just two standard RE’s per chassis. This means that for the SRX 5600, you must also purchase an additional SCB card, since it only comes with 1 standard, two for redundancy. On the SRX 5800 we provide two standard, 3 for redundancy so this isn’t required.
ii. Starting in JUNOS 10.2 we support dual data links. There is no additional hardware required for this feature, so long has you have two physical links per chassis to support the dual data links.

Just to add to Aditi's post, on SRX3K you cannot substitute a second RE in re1 slot. In order to support dual control link, SRX3K‐CRM is required for the second link.