I have two nodes bound to loopback interface address 127.0.0.1, one node is configured to only connect to other one. Unfortunately it is unable to download any blocks from other node. -debug=net on both reveals a bunch of details.
Client node debug.log (duplicate entries dropped):
2016-09-22 19:25:15 Added connection peer=268
2016-09-22 19:25:15 connection from 127.0.0.1:54414 accepted
2016-09-22 19:25:18 received: version (102 bytes) peer=268
2016-09-22 19:25:18 send version message: version 70012, blocks=287903, us=0.0.0.0:8333, peer=268
2016-09-22 19:25:18 sending: version (101 bytes) peer=268
2016-09-22 19:25:18 sending: verack (0 bytes) peer=268
2016-09-22 19:25:18 receive version message: /Satoshi:0.12.1/: version 70012, blocks=415389, us=0.0.0.0:0, peer=268
2016-09-22 19:25:18 sending: ping (8 bytes) peer=268
2016-09-22 19:25:18 initial getheaders (421144) to peer=268 (startheight:415389)
2016-09-22 19:25:19 sending: getheaders (997 bytes) peer=268
2016-09-22 19:25:20 received: verack (0 bytes) peer=268
2016-09-22 19:25:20 sending: sendheaders (0 bytes) peer=268
2016-09-22 19:25:20 received: getaddr (0 bytes) peer=268
2016-09-22 19:25:20 received: ping (8 bytes) peer=268
2016-09-22 19:25:20 sending: pong (8 bytes) peer=268
2016-09-22 19:25:20 received: sendheaders (0 bytes) peer=268
2016-09-22 19:25:20 received: pong (8 bytes) peer=268
2016-09-22 19:25:21 trying connection 127.0.0.1:8333 lastseen=0.0hrs
2016-09-22 19:25:21 Added connection peer=269
2016-09-22 19:25:21 send version message: version 70012, blocks=287903, us=0.0.0.0:8333, peer=269
2016-09-22 19:25:21 sending: version (101 bytes) peer=269
2016-09-22 19:25:21 socket recv error An established connection was aborted by the software in your host machine. (10053)
2016-09-22 19:25:21 disconnecting peer=269
2016-09-22 19:25:56 sending: addr (12153 bytes) peer=268
2016-09-22 19:27:18 sending: ping (8 bytes) peer=268
2016-09-22 19:27:18 received: pong (8 bytes) peer=268
2016-09-22 19:27:18 pong peer=268: Timing mishap, 28da2f9c49955968 expected, 28da2f9c49955968 received, 8 bytes
2016-09-22 19:27:18 received: ping (8 bytes) peer=268
2016-09-22 19:27:18 sending: pong (8 bytes) peer=268
2016-09-22 19:27:27 trying connection 127.0.0.1:8333 lastseen=0.0hrs
2016-09-22 19:27:27 Added connection peer=291
2016-09-22 19:27:27 send version message: version 70012, blocks=287903, us=0.0.0.0:8333, peer=291
2016-09-22 19:27:27 sending: version (101 bytes) peer=291
2016-09-22 19:27:27 socket recv error An established connection was aborted by the software in your host machine. (10053)
2016-09-22 19:27:27 disconnecting peer=291
2016-09-22 19:29:18 sending: ping (8 bytes) peer=268
2016-09-22 19:29:18 received: pong (8 bytes) peer=268
2016-09-22 19:29:18 pong peer=268: Timing mishap, 3ec10460bf8bca87 expected, 3ec10460bf8bca87 received, 8 bytes
2016-09-22 19:29:18 received: ping (8 bytes) peer=268
2016-09-22 19:29:18 sending: pong (8 bytes) peer=268
2016-09-22 19:29:22 trying connection 127.0.0.1:8333 lastseen=0.0hrs
2016-09-22 19:29:22 Added connection peer=311
2016-09-22 19:29:22 send version message: version 70012, blocks=287903, us=0.0.0.0:8333, peer=311
2016-09-22 19:29:22 sending: version (101 bytes) peer=311
2016-09-22 19:29:22 socket recv error An established connection was aborted by the software in your host machine. (10053)
2016-09-22 19:29:22 disconnecting peer=311
2016-09-22 19:31:18 sending: ping (8 bytes) peer=268
2016-09-22 19:31:23 trying connection 127.0.0.1:8333 lastseen=0.0hrs
2016-09-22 19:31:23 Added connection peer=332
2016-09-22 19:31:23 send version message: version 70012, blocks=287903, us=0.0.0.0:8333, peer=332
2016-09-22 19:31:23 sending: version (101 bytes) peer=332
2016-09-22 19:31:23 socket recv error An established connection was aborted by the software in your host machine. (10053)
2016-09-22 19:31:23 disconnecting peer=332
2016-09-22 19:31:29 trying connection 127.0.0.1:8333 lastseen=0.0hrs
2016-09-22 19:31:29 Added connection peer=333
2016-09-22 19:31:29 send version message: version 70012, blocks=287903, us=0.0.0.0:8333, peer=333
2016-09-22 19:31:29 sending: version (101 bytes) peer=333
2016-09-22 19:31:29 socket recv error An established connection was aborted by the software in your host machine. (10053)
2016-09-22 19:31:29 disconnecting peer=333
Host (proxy) node debug.log:
2016-09-22 19:25:15 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:25:15 trying connection 127.0.0.1:8343 lastseen=0.0hrs
2016-09-22 19:25:15 Added connection to 127.0.0.1:8343 peer=1
2016-09-22 19:25:15 send version message: version 70012, blocks=415389, us=0.0.0.0:8333, them=0.0.0.0:0, peer=1
2016-09-22 19:25:15 sending: version (102 bytes) peer=1
2016-09-22 19:25:18 received: version (101 bytes) peer=1
2016-09-22 19:25:18 sending: verack (0 bytes) peer=1
2016-09-22 19:25:18 sending: getaddr (0 bytes) peer=1
2016-09-22 19:25:18 receive version message: /Classic:1.1.1/: version 70012, blocks=287903, us=0.0.0.0:0, peer=1, peeraddr=127.0.0.1:8343
2016-09-22 19:25:18 added time data, samples 2, offset +0 (+0 minutes)
2016-09-22 19:25:18 sending: ping (8 bytes) peer=1
2016-09-22 19:25:18 received: verack (0 bytes) peer=1
2016-09-22 19:25:18 sending: sendheaders (0 bytes) peer=1
2016-09-22 19:25:18 received: ping (8 bytes) peer=1
2016-09-22 19:25:18 sending: pong (8 bytes) peer=1
2016-09-22 19:25:19 received: getheaders (997 bytes) peer=1
2016-09-22 19:25:19 Ignoring getheaders from peer=1 because node is in initial block download
2016-09-22 19:25:20 received: sendheaders (0 bytes) peer=1
2016-09-22 19:25:20 received: pong (8 bytes) peer=1
2016-09-22 19:25:21 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:25:26 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:25:32 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:25:38 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:25:44 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:25:50 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:25:55 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:25:56 received: addr (12153 bytes) peer=1
2016-09-22 19:26:01 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:26:05 connection to 71.96.128.213:8333 timeout
2016-09-22 19:26:05 trying connection 61.192.153.112:8333 lastseen=4957.4hrs
2016-09-22 19:26:07 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:26:13 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:26:18 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:26:24 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:26:30 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:26:36 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:26:41 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:26:47 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:26:53 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:26:59 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:27:04 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:27:05 connection to 61.192.153.112:8333 timeout
2016-09-22 19:27:06 trying connection 89.46.74.198:8333 lastseen=3293.1hrs
2016-09-22 19:27:10 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:27:16 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:27:18 received: ping (8 bytes) peer=1
2016-09-22 19:27:18 sending: pong (8 bytes) peer=1
2016-09-22 19:27:18 sending: ping (8 bytes) peer=1
2016-09-22 19:27:18 received: pong (8 bytes) peer=1
2016-09-22 19:27:18 pong peer=1: Timing mishap, eb132390474fe64e expected, eb132390474fe64e received, 8 bytes
2016-09-22 19:27:22 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:27:27 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:27:33 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:27:39 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:27:45 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:27:50 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:27:56 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:28:02 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:28:06 connection to 89.46.74.198:8333 timeout
2016-09-22 19:28:06 trying connection 167.160.36.104:8333 lastseen=0.7hrs
2016-09-22 19:28:07 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:28:08 Added connection to 167.160.36.104:8333 peer=2
2016-09-22 19:28:08 send version message: version 70012, blocks=415389, us=0.0.0.0:8333, them=167.160.36.104:8333, peer=2
2016-09-22 19:28:08 sending: version (102 bytes) peer=2
2016-09-22 19:28:08 trying connection 52.192.133.208:8333 lastseen=4903.4hrs
2016-09-22 19:28:08 received: version (122 bytes) peer=2
2016-09-22 19:28:08 sending: verack (0 bytes) peer=2
2016-09-22 19:28:08 sending: getaddr (0 bytes) peer=2
2016-09-22 19:28:08 receive version message: /BitcoinUnlimited:0.12.1(EB16; AD4)/: version 80002, blocks=431021, us=85.254.73.225:39984, peer=2, peeraddr=167.160.36.104:8333
2016-09-22 19:28:08 added time data, samples 3, offset +9 (+0 minutes)
2016-09-22 19:28:08 sending: ping (8 bytes) peer=2
2016-09-22 19:28:08 initial getheaders (431019) to peer=2 (startheight:431021)
2016-09-22 19:28:08 sending: getheaders (997 bytes) peer=2
2016-09-22 19:28:08 received: verack (0 bytes) peer=2
2016-09-22 19:28:08 sending: sendheaders (0 bytes) peer=2
2016-09-22 19:28:08 received: ping (8 bytes) peer=2
2016-09-22 19:28:08 sending: pong (8 bytes) peer=2
2016-09-22 19:28:08 received: addr (31 bytes) peer=2
2016-09-22 19:28:09 received: pong (8 bytes) peer=2
2016-09-22 19:28:10 received: headers (163 bytes) peer=2
2016-09-22 19:28:10 Requesting block 0000000000000000031a5aacde68a9c10ab102fc0706582f8a2e92982986f1e0 (415390) peer=2
2016-09-22 19:28:10 Requesting block 000000000000000003e42583356cda7652363ed5087c324cb2f3ab26d139d747 (415391) peer=2
2016-09-22 19:28:10 Requesting block 000000000000000003e4cebd4f63a40487aaba72eb9ec0c804cec6ad8a42b6a4 (415392) peer=2
2016-09-22 19:28:10 Requesting block 000000000000000003590b54627291773f30c83610dd28661b288c31ac2794ca (415393) peer=2
2016-09-22 19:28:10 Requesting block 0000000000000000010537a0e115b881d81f3a7757975fe69386d57a5cad3d39 (415395) peer=2
2016-09-22 19:28:10 Requesting block 00000000000000000084b245f3536ac27b8970a8b24790aa1586d8c327694f0a (415396) peer=2
2016-09-22 19:28:10 Requesting block 0000000000000000047d3c54778f24f16fd7545deeb4b86951c6412353756725 (415397) peer=2
2016-09-22 19:28:10 Requesting block 000000000000000005623a54c1768fa302fc0ff56981fe161112c56c8460daa0 (415398) peer=2
2016-09-22 19:28:10 Requesting block 0000000000000000050525e49d0241e6d7d11181f882c2cbb6dd4fcc5303fa74 (415400) peer=2
2016-09-22 19:28:10 Requesting block 0000000000000000001856e119c0b08cf3f570eea01c761bfebad81679a28fee (415401) peer=2
2016-09-22 19:28:10 Requesting block 000000000000000004698e6ecd0a4a7962f6d615b165c4d65da1ed2131e1b8db (415402) peer=2
2016-09-22 19:28:10 Requesting block 000000000000000001f53ea440b6e4ef89d783003e1365345bf117f354747349 (415404) peer=2
2016-09-22 19:28:10 Requesting block 000000000000000000ad413022c571a06611d3b41de5c9a204a588e54de423cd (415405) peer=2
2016-09-22 19:28:10 Requesting block 000000000000000000f0747d8703317b2648ccd4e04e9aff6c5782ae153a29ca (415406) peer=2
2016-09-22 19:28:10 Requesting block 00000000000000000042f4a5ad3e11a780de12aff12cc6db0d859cf4490e5e2e (415408) peer=2
2016-09-22 19:28:10 Requesting block 00000000000000000072292ffaeb4336b66259b9a19450f240dfda5ab90c2444 (415410) peer=2
2016-09-22 19:28:10 sending: getdata (577 bytes) peer=2
2016-09-22 19:28:13 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:28:19 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:28:25 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:28:30 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:28:36 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:28:42 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:28:48 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:28:54 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:28:59 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:29:05 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:29:08 connection to 52.192.133.208:8333 timeout
2016-09-22 19:29:09 trying connection 52.26.169.121:8333 lastseen=2648.8hrs
2016-09-22 19:29:11 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:29:17 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:29:18 received: ping (8 bytes) peer=1
2016-09-22 19:29:18 sending: pong (8 bytes) peer=1
2016-09-22 19:29:18 sending: ping (8 bytes) peer=1
2016-09-22 19:29:19 received: pong (8 bytes) peer=1
2016-09-22 19:29:19 pong peer=1: Timing mishap, 3ec0de2a3ab3bc73 expected, 3ec0de2a3ab3bc73 received, 8 bytes
2016-09-22 19:29:22 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:29:28 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:29:34 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:29:40 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:29:45 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:29:51 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:29:57 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:30:03 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:30:08 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:30:09 sending: ping (8 bytes) peer=2
2016-09-22 19:30:09 connection to 52.26.169.121:8333 timeout
2016-09-22 19:30:09 trying connection 72.192.73.43:8333 lastseen=3113.8hrs
2016-09-22 19:30:14 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:30:19 received: block (999837 bytes) peer=2
2016-09-22 19:30:19 received block 0000000000000000031a5aacde68a9c10ab102fc0706582f8a2e92982986f1e0 peer=2
2016-09-22 19:30:20 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:30:26 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:30:31 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:30:37 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:30:43 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:30:49 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:30:54 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:31:00 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:31:06 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:31:09 connection to 72.192.73.43:8333 timeout
2016-09-22 19:31:10 trying connection 52.26.170.72:8333 lastseen=167.8hrs
2016-09-22 19:31:10 Added connection to 52.26.170.72:8333 peer=3
2016-09-22 19:31:12 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:31:17 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:31:23 failed to find an eviction candidate - connection dropped (full)
2016-09-22 19:31:29 failed to find an eviction candidate - connection dropped (full)
Doesn't that means if all nodes are tricked into desynced or initial sync state bitcoin network might halt completely?