[SOLVED] two nodes in cassandra are not gossiping to each other

Node0:
configuration.yaml file:
cluster_name: 'ServerCluster'
num_tokens: 256
Seeds: ""
listen_address: 10.104.0.15
rpc_address: 10.104.0.15
auto_bootstrap: false
endpoint_snitch: GossipingPropertyFileSnitch

cassandra-env.sh file : JVM_OPTS="$JVM_OPTS -java.rmi.server.hostname=10.104.0.15"
cassandra-rackdc file: dc=DC1rack=RAC1

Node1:
configuration.yaml file:
cluster_name: 'ServerCluster'
num_tokens: 256
Seeds: "10.104.0.15"
listen_address: 10.104.0.20
rpc_address: 10.104.0.20
auto_bootstrap: true
endpoint_snitch: GossipingPropertyFileSnitch

cassandra-env.sh file : JVM_OPTS="$JVM_OPTS -Djava.rmi.server.hostname=10.104.0.20"
cassandra-rackdc file: dc=DC1rack=RAC1

Node0 is up and fine
Node1 error:

INFO  00:03:44 OutboundTcpConnection using coalescing strategy DISABLED
INFO  00:03:45 Handshaking version with /10.104.0.15
ERROR 00:04:16 Exception encountered during startup
java.lang.RuntimeException: Unable to gossip with any seeds
    at org.apache.cassandra.gms.Gossiper.doShadowRound(Gossiper.java:1333) ~
[apache-cassandra-2.1.10.jar:2.1.10]
    at org.apache.cassandra.service.StorageService.checkForEndpointCollision
(StorageService.java:540) ~[apache-cassandra-2.1.10.jar:2.1.10]
    at org.apache.cassandra.service.StorageService.prepareToJoin(StorageServ
ice.java:788) ~[apache-cassandra-2.1.10.jar:2.1.10]
    at org.apache.cassandra.service.StorageService.initServer(StorageService
.java:720) ~[apache-cassandra-2.1.10.jar:2.1.10]
    at org.apache.cassandra.service.StorageService.initServer(StorageService
.java:611) ~[apache-cassandra-2.1.10.jar:2.1.10]
    at org.apache.cassandra.service.CassandraDaemon.setup(CassandraDaemon.ja
va:387) [apache-cassandra-2.1.10.jar:2.1.10]
    at org.apache.cassandra.service.CassandraDaemon.activate(CassandraDaemon
.java:562) [apache-cassandra-2.1.10.jar:2.1.10]
    at org.apache.cassandra.service.CassandraDaemon.main(CassandraDaemon.jav
a:651) [apache-cassandra-2.1.10.jar:2.1.10]
java.lang.RuntimeException: Unable to gossip with any seeds
    at org.apache.cassandra.gms.Gossiper.doShadowRound(Gossiper.java:1333)
    at org.apache.cassandra.service.StorageService.checkForEndpointCollision
(StorageService.java:540)
    at org.apache.cassandra.service.StorageService.prepareToJoin(StorageServ
ice.java:788)
    at org.apache.cassandra.service.StorageService.initServer(StorageService
.java:720)
    at org.apache.cassandra.service.StorageService.initServer(StorageService
.java:611)
    at org.apache.cassandra.service.CassandraDaemon.setup(CassandraDaemon.ja
va:387)
    at org.apache.cassandra.service.CassandraDaemon.activate(CassandraDaemon
.java:562)
    at org.apache.cassandra.service.CassandraDaemon.main(CassandraDaemon.jav
a:651)
Exception encountered during startup: Unable to gossip with any seeds
WARN  00:04:16 No local state or state is in silent shutdown, not announcing     shu

tdown INFO 00:04:16 Waiting for messaging service to quiesce INFO 00:04:16 MessagingService has terminated the accept() thread

Then I changed the seeds(because saw a solution in stackoverflow) for
Node0:
Seeds: "10.104.0.15,10.104.0.20"
Node1:
Seeds: "10.104.0.20"

Node0 is fine
Node1 error:

INFO  00:25:36 Thrift API version: 19.39.0
INFO  00:25:36 CQL supported versions: 2.0.0,3.2.1 (default: 3.2.1)
INFO  00:25:36 Initializing index summary manager with a memory pool size of    101
MB and a resize interval of 60 minutes
INFO  00:25:36 Loading persisted ring state
ERROR 00:25:36 Exception encountered during startup
java.lang.IllegalStateException: Shutdown in progress
    at java.lang.ApplicationShutdownHooks.add(ApplicationShutdownHooks.java:
66) ~[na:1.8.0_60]
    at java.lang.Runtime.addShutdownHook(Runtime.java:211) ~[na:1.8.0_60]
    at org.apache.cassandra.service.StorageService.initServer(StorageService
.java:718) ~[apache-cassandra-2.1.10.jar:2.1.10]
    at org.apache.cassandra.service.StorageService.initServer(StorageService
.java:611) ~[apache-cassandra-2.1.10.jar:2.1.10]
    at org.apache.cassandra.service.CassandraDaemon.setup(CassandraDaemon.ja
va:387) [apache-cassandra-2.1.10.jar:2.1.10]
    at org.apache.cassandra.service.CassandraDaemon.activate(CassandraDaemon
.java:562) [apache-cassandra-2.1.10.jar:2.1.10]
    at org.apache.cassandra.service.CassandraDaemon.main(CassandraDaemon.jav
a:651) [apache-cassandra-2.1.10.jar:2.1.10]
java.lang.IllegalStateException: Shutdown in progress
    at java.lang.ApplicationShutdownHooks.add(ApplicationShutdownHooks.java:
66)
    at java.lang.Runtime.addShutdownHook(Runtime.java:211)
    at org.apache.cassandra.service.StorageService.initServer(StorageService
.java:718)
    at org.apache.cassandra.service.StorageService.initServer(StorageService
.java:611)
    at org.apache.cassandra.service.CassandraDaemon.setup(CassandraDaemon.ja
 va:387)
    at org.apache.cassandra.service.CassandraDaemon.activate(CassandraDaemon
.java:562)
    at org.apache.cassandra.service.CassandraDaemon.main(CassandraDaemon.jav
a:651)
Exception encountered during startup: Shutdown in progress

So can you help me to get out this chicken and egg problem? Than you in advance

even I followed the datastax link https://academy.datastax.com/courses/ds210-datastax-enterprise-operations-and-performance-tuning/multiple-data-centers-multiple-0
where he just changes the clustername,listen_address, rpc_address and seeds and when he types nodetool status he was able to see both of them but when i follow the same I see only its status in it respective server