Interface jsrv.1 is always associated to IP address 128.0.0.127.
jsrv up up
jsrv.1 up up inet 128.0.0.127/2
An archive at SourceForge has the below command output snippet that shows a connection between 128.0.0.127 and port 6343 (sFlow port)1:
tcpdump -v udp port 6343 -s 1500:
11:52:07.624977 IP (tos 0x0, ttl 254, id 5728, offset 0, flags [none],
proto UDP (17), length 1484)
10.1.1.1.60578 > collector.6343: sFlowv5, IPv4 agent 128.0.0.127,
agent-id 17, seqnum 38496, uptime 1963373233, samples 8, length 1456
flow sample (1), length 196,
<...snipped...>
There is a Juniper Knowledge Center (cached google link) article that indicates there are 2 separate programs supporting the sFlow function, an agent and a collector.
The sFlow monitoring system consists of an sFlow agent embedded in the
EX Switch and has a centralized collector. The sFlow agent’s two main
activities are random sampling and statistics gathering. It combines
interface counters and flow samples and sends them across the network
to the sFlow collector. The sFlow collector uses the sFlow agent’s IP
address to determine the source of the sFlow data. This KB article
explains how the EX Switch assigns the IP address to the sFlow agent.
The jsrv interface appears to be a built-in Juniper sFlow sub-system that allows communication between the internal collector and agent.
1Note, this is the only connection to 128.0.0.127 I've been able to locate.
With help from our service provider we've been able to localise the problem. The idea I had in my last comment proved correct: the difference between fast ethernet and gigabit ethernet was the source of the problem.
The reason for dropping connections, undeliverable packets and segmented packets was a mismatch in link mode between the fiber switch and the SRX - they hardcoded their port to 100m full duplex, but the SRX had automatic negotiation, which resolved to 100m half duplex.
The problem was further complicated by Juniper's odd configuration of speed and link mode. Just setting these configuration options wasn't enough:
speed 100m;
link-mode full-duplex;
This configuration was accepted, but when running show interfaces ge-0/0/0, it still showed:
Link-level type: Ethernet, MTU: 1514, Link-mode: Half-duplex, Speed: 100mbps,
Apparently, you have to explicitly disable auto-negotiation:
speed 100m;
link-mode full-duplex;
gigether-options {
no-auto-negotiation;
}
In the end, I found that this guy had the exact same problem (and the solution!)
Thanks for all your help.
Best Answer
A physical interface can consists of multiple logical interfaces, each called a
unit. Each unit has a number as a unique identifier. The0just refers to the first logical interface.It's good practice (but not required) to keep the unit number in sync with the VLAN id. In that case
unit 0often refers to the untagged interface.family inetrefers to the IPv4 address family. An interface can have configuration for multiple address families, each with their own specific configuration and purpose.